The MiniAmp 2.0

This time I want to show you my new MiniAmp 2.0. It is an approximately 1.5W-2W guitar amplifier with an ECC99 push-pull poweramp. The MiniAmp 2.0 was build by me because I loved how the MiniAmp Number 1 came out and so I wanted to build another little amp just a little bit different soundwise and a bit more versatile.
This one now got two 12AX7s in the preamp and provides a tone stack with treble, middle and bass plus a volume control. The second 12AX7 here serves as a third gain-stage and a cathodyne phase inverter which feeds the ECC99 triodes with their phase inverted signals. The two 12AX7s not only allow you to compensate the gain-loss of the tone stack and to use a PI but also provide you with an overall different sound and overdrive behavior than an amp with just one 12AX7 like the MiniAmp Number 1. In addition to that the use of a phase inverter feeding the ECC99 over a self-splitting ECC99 poweramp delivers more output and therefore more clean headroom. The preamp is inspired by the Vox Night Train (which seems to be inspired by the Blues Express variant of the Trainwreck Express). For the output-transformer I used a Hammond 125B and for the power-transformer I used a toroidal transformer with secondary: 200V 0.1A and 6.3V 1.5A which I found HERE.

So how does it sound? Well it sounds like a smooth, rockin’, warm, creamy, twangy … naaaa, no words can describe a sound better than hearing it for yourself!

Here are some samples:

And here are some pictures:

Some pictures from the inside:


And finally here is the schematic:


450 Responses to “The MiniAmp 2.0”

  1. Good job!

  2. Looks and sounds great. I’ll be giving this a try. What are your voltages at A, B, C and D?

    • I’ve looked into my notes and there I wrote down A: 260V B: 217V C: 209V D: 205V But I’m not sure if these are the voltages of the final circuit… I will measure them again and then I will update the schematic with the voltages.

      • The real voltages are A: 235V B: 211V C: 203 D: 199V. I added them to the schematic. My previously posted votage for A seems to be a little bit wrong, I must have misread it…

  3. Thank you for doing this. It is greatly appreciated.

  4. Do you have the list of components?
    Good Job!!

  5. Jesse van Oort Says:

    Hi, great work!

    I’d like to give this a try, should work alright with your scheme.
    One question though: do you have the pin numbers for the valves in the scheme?


    • The pins on every of these double triode tubes are from the gap clockwise: (1) Anode [Triode 1]; (2) Grid [Triode 1]; (3) Cathode [Triode 1]; (4) Heater Filament; (5) Heater Filament; (6) Anode [Triode 2]; (7) Grid [Triode 2]; (8) Cathode [Triode 2]; (9) Heater Filament Center
      You can find this in every datasheet of those tubes, for example here:

      greets 🙂

  6. Pablo Cholbi Alenda Says:

    This is a really cool project. I am very interested in your Miniamp 2.0 and your proximity wah, I am going to build them when I have the time. Could you tell me what enclosure you used for the Miniamp 2.0? Is it on

    Thanks for sharing.

  7. hi thank you for the great job. my question is : would it be difficult to add a gain with separate volume, just like night train? maybe taking off the middle eq..hearing the night train seems has more gain, but it would be good to have more clean volume without distortion deciding the amount of gain…thanks

    • It’s not difficult to add a master-volume. You could use the Night Trains approach with a stereo potentiometer after the phase inversion for example. If you like to build it in an enclousure with a similar size, you could also put the MV on the back of the amp for example. I personally wouldn’t take the middle eq potentiometer out, because it has so much influence on the overall sound. You would loose a lot of flexibility.

  8. How can I make the power transformer work on a 110v line in the US? I would imagine a simple voltage doubler?

    • The best solution would be to find a transformer that provides similar secondary voltages (about 200V 0.1A and 6.3V 1.5A) with a primary voltage of 110V.

  9. Unfortunately I have already ordered (and received) the transformer thinking I could figure something out, and because it was cheaper than anything else I could find. After soon some research I found a 110/120v to 220/240v converter, here:

    Think it will it work?

  10. Trevor Says:

    Hey this amp sounds AWESOME!! I am in the process of building it, using the schematic you have listed on this site. I am just wondering if you have made any changes or tweaks to the schematic in any way. I love the sound clips I heard and I just wanted to make sure that this schematic matches the clips Ive heard. Also I have a question about Pot 2 (500 ohms). Im just wondering if this is 500 ohms or is that a typo, and also Im not sure what this pot does (is it for biasing the power tubes?). If its for biasing is there a bias voltage that I should be shooting for. Also Im going to use audio taper for Pot 1 (1M), Im assuming this is the volume pot. Is there any other pots that should be audio taper?
    Thanks again…..I love the sound of this amp…..great job! How does the bass end of the amp translate live (is there enough?)

    • Hi, thanks!
      Yes, the schematic matches the clips. Pot 2 is a 500 ohm trimmer pot to bias the ECC99, but I’ve already replaced it with a fixed 150 Ohm resistor in my build, which seemed to be a nice sounding and suitable bias point to me.
      I also went with an audio taper pot for volume, but for the tonestack I went with linear pots, so far.
      The bass response is really great for such a tiny amp design.


      • Trevor Says:

        Dude your Les Paul clip really shows the lower end capabilities of this amp. I was between this circuit and the blues express schematic that uses a 12au7 power amp. After hearing the clips I was sold on yours. Great circuit design and implementation.

      • You should definitely go with the ECC99. I tried both in my first miniamp and the ECC99 sounds way better than the 12AU7, especially when it comes to bass response.

  11. Hi, me again. I’m pretty sure I have all the pots sorted out to what they’re doing, (1 is volume, 3 is treble, 4 is mids, 5 is bass), is this correct?

  12. Guess who!? Yep, me again. Completed the circuit the other day. and surprise surprise, the heaters aren’t getting enough current due to that power converter I had spoke about a few weeks ago. I did some more research and found this:
    The first secondary is 200v/40ma, the second is 12v/1A. I’ll of course have to change around the power supply for the filaments. But will the 200v/40ma be sufficient?
    I apologize for asking all these questions, I’m just a high school student! 😉
    Thank you for all your help, and for the great design!

  13. Confused that transformer with this one:

    Would like to know which one would be best.

    • Sry but both of them are a bit short, search for something that delivers at least 60ma at 200V or close and 1.5A for 6.3V or 0.8A for 12.6V heater supply.

  14. Then the Hammond 263AX should work, correct? It meets the specs. I have a small transformer i could use for the filaments.

  15. Hey just wondering if I can use a Hammond 125C instead of the 125B as the output transformer.

  16. Another couple of questions for you. I am planning on using 2 watt resistors for the power supply section (between the filter caps) and for the plate resistors. Are 1/4 watt good for everything else or should I use 1/2 watt (im using metal film)? For the caps Im using caps rated at 450V for the power supply section, Im just wondering what voltage rating I should use on the electrolytics that are in parallel with the cathode resistors. Also is there special wire I should use for this build…..I usually use stranded/bonded wire from smallbear electronics 24 gauge (for pedal builds). I think the voltage rating on this wire as well as there 22 gauge is 300V (wondering if this is rated high enough). Also should the ground buss from the power supply section be connected to the ground buss of the amp section, and then to the chassis ( I am going to be perf-boarding the entire build)?

    • 1/4W resistors everywhere else should be enough. For the cathode bypass caps everything from 16V rating should work. The voltage rating for the wiring should be higher than the highest voltage of the power supply so if your 300V are right that should be enough, but you should use some thicker wire for the heater wiring, because of the high current going on there. There are many different approaches for proper grounding an amp for less noise. If your using two ground busses, I would let them both connect two the chassis at the same location.

  17. Sorry for all of the questions, but is the pot lug numbering in the tone section from top to bottom 3,2,1. I notice the wiper arrow is pointing in the downward direction in the tone section and for the volume pot. For the bias pot it is pointing up, does this denote a reversal of numbering like 1,2,3? Thanks again,

    • The schematic was not drawn with the numbering in mind. But 3,2,1 from top to bottom on the tone and volume pots is right and 1,2,3 from top to bottom on the bias pot should be right too.

  18. Just to help some of our US friends out, I found this Toroidal transformer, which seems to be just right for Voltage/amperage requirements. It is abit bigger in size and weight than yours (refer to the spec sheet for details).

    • Thanks for posting!

    • I used this transformer for my build. It is large at 4.5in x 2in. It also has two inputs and four outputs.

      • Robert Lange, Jr. Says:

        I’m using this same transformer for my build. But I’m not sure how to wire it. Do you group the input leads together and the output leads together? Or do you pick one input pair, one 200v output pair, and one 6.3v output pair and then insulate the remaining leads (i.e. the unused leads)? Please advise

  19. Hey just a thought here, I know that the 18K feedback loop resistor, helps to attenuate bass, I was thinking about using a DPDT on/on switch to either put the feedback loop in or to bypass it with straight signal (without the 18K resistor), does this seem like a good idea in terms of giving some variation to the sound?

    • Yes, try what you like. The Vox Night Train, for example, uses the opposite approach, by taking out the feedback loop and rebiasing the two stages. Look at the the NT-15s schematic for more details…

      • Another question I am using the Hammond 125C, and am wondering what secondary numbers I should use for running 8 and 16 ohms as opposed to 4 and 8 ohms which is on your schematic. Thanks again you really have been super helpful.

      • You should use lug 3 & 5 for 8 ohms and 2 & 5 for 16 ohms. Therefor you should connect lug 5 to ground and switch between 3 and 2.

  20. Hello. I am currently in the process of testing a PCB for this, would you like the EAGLE file when it is done? It is a double sided board, since that is the only way the parts could fit on the free version of Cadsoft Eagle. Or I can give it to you whenever you want, and you can modify it to your liking.

    • Nice, yes I would be interested! Are you wiring the heaters off-board or are they included on the board? You should be carefull with the layout to avoid hum and feedback, but you’re propably aware of that.

      • The heaters are not on the PCB. The wires will be coming directly from the power supply board. I replied to your email.

    • Hi ,did you ever get the eagle file for the miniamp2.0

  21. This is a really cool Amp, I’d like to give this a try.
    To build the amp it would be nice to have the PCB made by Devan. Can you make it available on this site?
    Tanks for sharing knowledge.

    • It’s up to Devan… If he likes to have it posted here, I would add it to this site… As far as I know Devan is still in the process of developing and testing the PCB.

      • Devan Says:

        The PCB ended up not working out very well. I have begun summer vacation, and I’ll try to work on getting a better, single sided design made.

  22. Jason Lilly Says:

    Amazing! This is the best sounding small amp I’ve come across. Any chance you could draw up a layout ?
    Also, I was wondering if it’s possible to run two of these with one PT and in one enclosure for a stereo setup.

    • Hi, most of the amp is wired point-to-point, so a layout wouldn’t look much different than the schematic. All you need to get it wired is the schematic.
      You could use one PT if it can handle the extra current, the one I used does not. 🙂 But this circuit is not designed for high fidelity audio playback, if that is what you’re aiming for?

  23. Nice work!
    Is there a high resolution schematic for the Miniamp2, comparable to what you provided for the Miniamp1?

  24. I started collecting the parts for this amp. But a have question on the potentiometers. Are these linear or logarithmic? I suppose P2 is a Lin, but what are P1,3,4,5? Log/Lin?

  25. Ok Ive built the mini-amp, and can definitely say, that this is the amp to build, if your looking for a low wattage recording amp. The cleans are chimey and beautiful, and the overdriven to fuller gain tones are rich, harmonic, and can be perfectly voiced. I just got my recording mic back from church, and I plan to post a demo clip, but honestly the youtube clips that FcKw put up, really do the amp justice, and live there is more goodness to be experienced. I am directly comparing my Orange Tiny Terror to the mini-amp 2.0 and can say that I like the mini-amp better, as I feel it is more flexible and tweaker friendly.

  26. great amp!!i’m ordering the parts! I’m an electronic ignorant but i’ve made several effects. this is my first attempt in high voltage! so: firsth thanks, second: sorry for my english! (i’m italian) third: sorry for my following question: what’s for p2? it’s a gain pot?

    • No, it’s a trimpot to set the bias of the output tube. Please be careful while handling with high voltages! They can even still be there while the amp is unplugged!

  27. thanks a lot! don’t worry! the firsth switch on attemp will be done by a friend of mine who’s expert! so can I use a 150r res instead the trimmer as you have done?

  28. I am going to build this amp. It is the best sounding after researching the internet for a week, 2 hours a day.

    1.) you should update the schematic and add like 220k resistor across first 100u capacitor in the power supply, so it would drain those capacitors when unplugged, so nobody will get shocked when tweaking the amp. I saw many amps with resistor like this.

    2.) is that 1M pot really a volume or is it just a gain?

    3.) should master volume be added after the phase inverter(stereo pot) or could it be before phase inverter (after 100n cap)
    I am aiming for option of clean preamp, but could clip the power stage and opposite

    4.) is the tone stack functionable or is it like on most amps where turning a knob 1/4 of a turn makes really no difference.

    5.) why are there pull down resistors on heater wires?

    6.) what is better: toroidal transformer or classical?

    • Nice to hear. 🙂

      1) I won’t do that, you should always check the voltages before you work on an amp! Even if you’ve got such a bleeder resistor installed, you can’t assume that it’s working properly or that the time since you switched your amp off was enough for that resistor to discharge the caps. So this resistor would be no advantage, it would be nothing but a false security presumption. Everyone who wants to tweak or even build an amp should be aware of the lethal voltages and should know about how to measure them and how to discharge the caps manually.

      2) It is both… old school. 🙂

      3) I’d take the stereo pot.

      4) The tonestack is very effective, if you find out you don’t like the control curve, simply try another potentiometer characteristic.

      5) they create an artificial center tap for the heater supply, so they reduce hum.

      6) Both are equally good circuit-wise, but especially for my tiny builds the toroidal transformer has the advantage of a lower exterior magnetic field and therefore interferes less with the other components on the chassis.

  29. Giuseppe Costa Says:

    Hello. Great project. I was thinking to add a second ECC99 in push-pull mode and use a little bigger power & output transformers to reach a 4 watts output. According to your experience, do you think it is worth to apply this changes or it is better to build the amp as is ? Would more power affect the tone and the overall flexibility of the amp ? Thank you.

    • Hi, I just had a similar thought some days ago for a new project. 🙂 I have no expierences with a four triode output stage at all, so I can’t really tell you about overall tonal changes. You should definitely get a little bit more headroom, but therefore the onset of the overdrive will raise to a higher volume level. I think you should try where it gets you with this preamp and the extra ECC99 added, perhaps you could start with one ECC99 and than add the second if you lack headroom, but I know that this is difficult to plan, because of chassis space and transformer properties…

  30. Hey,

    what a great amp.
    Do you have the list of components- I’m a newbie and would like to give this one a try.
    Can you estimate the total cost of this amp?


    • Hi,
      sry, I don’t have a list, but its simply everything that’s on the schematic and some screws, tube sockets and a chassis. 😉 I think it was something a little bit under 100 euro that I paid for the parts here in europe.
      If you’re a newbie be aware of the lethal voltages!

  31. Another question.

    Why did you put so big resistor values(10k,4k7) after rectification? I usually see only around 1k there in other amps.

    • They are needed to get the 50/60 cycle hum filtered with those 22uF capacitors. The amps you saw probably had bigger filter caps.

  32. thanks for that FcKw,
    what type of caps do you recommend? electrolytic? type of bridge rectifier? recommended brands… many thanks for your patience and your help


  33. I see you used highest voltage (A) on output transformer and the lowest voltage (D) on preamp tube. I saw many amps that had that wired the opposite. Any reason for that or it doesn’t matter?

    • What about an example? All guitar amplifiers I know use the higher voltage for the output stage and lower for the preamp. That’s because of two reasons, the poweramp often needs higher voltages, to be as efficient as it can be, the preamp however doesn’t need that high voltages. Second reason is the preamp needs a better filtered voltage supply (wich is the reason for the voltage drop in the first place). That is because of the bad signal-to-noise ratio at the input, all 50/60s cycle hum that would get in the first stages of the preamp would be amplified by the following stages, but at the poweramp the signal-to-noise ratio isn’t that critical anymore.

      • Sorry, I messed things up. It is only one possible way to wire it.

        Oh yes – I tried both master volumes – pre and post phase inverter and I like post PI much more. But now I have one potentiometer hole in the case, so I figured that it would be cool to have Presence control. (like Fender bassman, twin..). It is basically 20-50k resistor from speaker out connected to 5k pot with 100n cap. But Where do I return the signal? Do I need to eliminate current negative feedback loop? Or Do I feed it directly between that R21 and R24?

      • I never tried a feedback loop with a cathodyne PI, but I would do it like you said and try it with and without the preamps feedback loop. You made two holes for two master volumes?

        P.S. Why do you keep changing your name? it’s a little bit confusing… 😀

  34. McgYver Says:

    Why are you feeding Phase Inverter through 1M ohm resistor(R25)? Shouldn’t be there a direct connection without it? Why is it there? is it some sort of volume control? Should i remove it(R25 and R26) if I make pre phase inverter volume control?

    • The 1M grid stopper prevents blocking distortion and the frequency-doubling effect of cathodyne PIs. It’s no volume control.

      • Why did you put that grid stopper in? Because night train schematic doesn’t have one?

        If I use one of these calculators

        Grid stopper so big has terrible frequency responce? Aren’t grid stoppers normally on 10k-100k range?

        Just curious on how you noticed that so big grid stopper is neded.

        BTW I am building this amp again, because my power amp collapsed and squealed than died and now I am putting in ecc99.

      • I already wrote you why I put it in. Try yours without it and you’ll hear why. If it would be up to me the night train should have one, too. 😀 I got this idea from Merlin Blencowes “designing tube preamps…” book.
        The frequency response you can calculate on your linked site is for a triode wired as a gain stage, but not for one wired as a cathodyne PI. On a cathodyne PI the input capacitance is much lower than on a gain stage, so the treble rolloff isn’t noticeable with the 1M grid stopper.

  35. Sorry, I use 3 computers(work, home,workshop), and I didn’t notice different names.

    I will try everything and report.

    • oh, ok. I was just wondering. 🙂

      • I tested the amp today I didn’t managed to add presence control, because amp started to oscillate with sound like that 8 bit games. With or without current feedback loop. Without presence control it is dead quiet. I used shielded cables.

        (BTW I have russian 6P1P for the output for more power, basically whole poweramp is different)

        But I find the distortion very harsh. Whole amp under distortion sounds fizzy and lacks bass.

        I am using same transformer toroid. Does your get hot? Because mine is near its limit and it gets hot.

      • Could be, that it’s getting warm, but not really hot. The harshness and bass response could be the result of your different tube choice, I tried a 12AU7 first in my first Miniamp and it was the same problem with the lacking bass response happening there.

  36. Bass exists nicely on clean, but when you set gain bit more (master volume very low, so no power tube distortion) then bass is just gone. Sounds harsh and fizzy. Probably messed some component value. Will check tomorrow.

  37. Now I am finishing my amp. What bias point did you choose. What current on the pot P2? I see that you replaced it with 150 ohm resistor.

  38. Dear FcKw,

    I have few more newbie questions…
    Thanks so much for helping out!

    1-for the nano caps like C13, C15…you don’t show a direction- doen’t it metters ?
    2- For the output transe, would hammond 125 A or C work as well?(the 125B is expensive)
    3- would this trans wok as well:
    4- what type of resistors woul you recommend: metal film or CC?

    Thanks again

  39. thanks for the link !
    25 euro is far cheeper then I’ve seen so far!

  40. thanks Tacoboy!
    So these caps wold be TANTALUM type?

  41. THanks Jule,
    But now you confused me.
    PT caps are 450V now which caps are 200 V and which are 16V+?

    also what do you think about this trafo?
    I’ve read good remarks about it


  42. Very interesting project. I already have a 269ex power transformer, will it be sufficient for this amp? What are the symptoms if the PT is slightly under rated? Thanks.

    • The transformer is absolutely fine for this project, but you should use a center tap rectifier design with 2 diodes with this transformer.

    • Hi, I’m using an 8 ohm speaker, but you could also wire the output transformer so that it works with 16 ohms. It’s up to you, perhaps you can go after what your other amps need (if you have some), to be able to use them with this speaker too.

  43. Is there a watt rating for r34,r15,r35,r36,r20,r29? Thank you!

  44. Thank you very much for sharing ! It’s a brillant job !!!
    It sounds great . Finally a good project ,we’ve been wanting to do something like this for a long time 🙂
    I think I will make a pcb and I will choose a bigger enclosure cause it’s hard to manage all those wires in a so little space and i don’t feel very safe (200 v)

    • Thanks, have fun building it. Perhaps you could share the PCB-layout sometime, I think there could be some others who would be very thankful for it. 🙂

  45. Caps c3,c10 and c18 electrolytic? voltage values? Thanks again!

  46. Yes, But can you please tell me what type of capacitor you used? Thanks again.

  47. Would this amp be OK to put into a completely enclosed cabinet?

  48. FcKw, Have you tried tube rolling with other preamp tubes? ie-12at7, 5751 ect? Thanks, Cory. Thanks for the schematic! Mine is built and works great!

    • I haven’t tried different tubes yet, but I got a nice email from Trevor (who also posted a great video-demo in the comments) where he wrote about his experiences with different preamp tubes in the MiniAmp 2.0 circuit:
      “… Now for some interesting finds, regarding preamp tubes. Putting a 12AU7 in V2 decreases the background “white noise” by about 50%. You still get plenty of gain on tap with a 12AX7 in V1. I however chose to put a 12AT7 (NOS RCA that I had) in V1 and a JJ 12AU7 in V2. I still get enough gain for my style of playing with even less noise floor. I also have more clean head-room. If you want a sparkly clean amp for Jazz or old style country than 2-12AU7’s fit the bill rather well. …”
      Thanks again, Trevor!

  49. Wow I havent been around here in awhile. Im glad to see that this amp is catching on. I’ve been told by alot of different musicians/guitar players that this amp sounds just as boutique as any of the low wattage boutique amps out there. I also have to say that I find the sound of this amp preferable to the sound of my bass-boost modified Orange Tiny Terror. Its a great platform as is…..I tried messing around with cap values here and there, but decided that stock was the best option. It takes alot to design a tube amp, but a whole lot more to have the ear to make it exceptional. This amp is exceptional. I highly recommend using a 12AU7 in V2, I was very happy with the lower noise floor, yet there is still more than enough gain on tap with a 12AX7 or AT7 in V1.

    • Seems weird replying to my own post, but I wanted to clarify that this amp is not a noisy amp! It is high gain and as such there will be a normal background noise floor. My reccommendations came out of the need for a super quiet stage/recording setup. You can use this amp live as long as you are using in-ear monitors, and are of course micing the speaker cabinet.

  50. Izzy Madhatter Says:

    Hello, gret work, I would like to build this amp. I have a very good toridial main transformer with a secondary coil with 230V. Is it possible to use this one if I increase the R34 resistor value?

    • I’d use that transformer and keep everything as is. 30V won’t make that much of a difference, mainly just a little bit more headroom.

  51. I put a 12at7 in v1 and a 12au7 in v2, both RCA nos. I cannot emphasize enough how much it has changed the tone and gain!!! It turned it into a completely different amp! The tone stack works much better with this combo of tubes!

  52. Izzy Madhatter Says:

    Hello, could S3 also be a single switch?

  53. Horst Annegret Says:

    What about adding a buffered parallel effects loop to the amp? Has anybody done this? Where would I add that? And how would I get the power supply for the IC buffers and maybe the effects circuit itself (I’m thinking of putting a belton reverb in the amp)? I guess the 6,3V AC can’t be used?

  54. Hi FcKw,

    I’m final about to assemble your amp 🙂
    I have few more Q:

    1- it looks like input J1 is connected both + and – to ground, is this correct?
    2- can I switch position between pot P4 and P5? (make more sense going from low to high )
    3- my tube sockets have a center lug in addition to the 9 other lugs- should I connect it to ground or just let it be?

    Thank you

    • Hi izhak,

      1- There is no + and -, just the sleeve connected to ground and a switch that switches the tip connection to ground if there is no plug inserted.
      2- Physically you can do what ever you want, but the connections are as they are shown in the schematic.
      3- Just leave it unconnected.


  55. There was a question about what speaker and cab I used for my video. It was a Jet City 112 cab with a stock emminence speaker.

  56. Hi. As of this time, I have the power supply section built. I checked all the wiring, but I am getting 307v at each point (A, B, C, D). Output of the transformer is 200V at 100mA. (in reality it produces about 216v)

    What could be causing this issue? I am using all 450v rated caps and 1-watt resistors, if it helps.


  57. Hi

    Finally finished putting all together- its amazing how clean your amp looks compared to mine !
    My amp doesn’t work yet 😦
    I’m trying to measure V across A, B C and D and get nothing, Im measuring between end of caps (+) and ground- am I doing it right?
    (I am getting 200 Vac from trafo)
    Is it possible that holding the solder iron too long at the end of the caps while soldering destroyed them?

    Thank again

    • Yes thats the right way to measure these points. Frying caps is possible, but unlikely. Try to check the power supplies connections again, especially the rectifier diodes and make sure the 200V AC wires are not shorted electrically anywhere.

  58. Thank you FcKw, found the fault in the PT- I now have a working Amp- Thank you so much for all the support !
    1 last question (hopefully)- my Bass Pot 1M is faulty- can I take it out of the circuit and connect P3 to P5 ? and if so do I keep C11 in?


  59. Hi FcKw,

    do you have a list of components that you used for this build? can you post please. I am going to try to build it.



  60. Paul

    I have a list on an excell file
    give me your email and i can send it


  61. Hi,

    I’ve been searching through the ‘net to find a relatively budget-friendly and simple to build tube amp project, and this seems to suit my needs rather well. However, I would like to know if it would be possible to add another power tube to increase the output wattage? How could this be done? Also, I would like to add a separate master volume while having the gain controlled separately – this should’nt be hard to do, right? And one last question – can the amp tolerate effect pedals? I like the the sound of tube distortion very much, but sometimes in some occasions pedals like Jemini cut it better – does this cause any negative effects?

    Thanks for the quick reply and a happy new year!

    • You can simply put another pair of triodes parallel to the two ECC99 triodes, with some extra grid resistors and cathode resistor/cap, but you have to consider a different biasing and the current that is drawn by the extra tube of course, actually I’m planning something similar for the future, too. 🙂
      A master volume is no problem, too. You can look for the Vox Night Train schematic on the internet which has a dual pot master volume after the phase inverter.
      The amp handles effects great as far as I have tested it…

      a happy new year to you too!

      • Following up on the post-PI master volume… In the regular Night Train the grid resistors for the power tubes are much lower than in your amp. Does that have more to do with the tube type or the MV implementation? What are the guidelines for sizing those resistors?

      • The grid stoppers are there to prevent blocking distortion and other unwanted distortion that can be caused by the cathodyne PI. They should not effect the implementation of the MV.

  62. Hi, i just finished building your amp, but used different transformers to the ones on the schematic. Power supply voltages are close enough to yours, but the output transformer is different. Its from an old PA system, and i have used it in a different 15W tube build and it works perfectly.

    The amp i built is quiet and seems to flick from no sound to a bit of sound over a 5 or 7 second period and then go quiet again. I’ve double checked all the wiring to the schematic, and I cant find a problem. Tried fresh tubes and no difference. Any ideas, and do you think getting the different transformers would fix it. I’m out of ideas.

    Oh yeah, the amp in your clips sounds AWESOME which is why i decided to build it. Best sounding small amp i’ve heard

    • Well, I feel stupid. I checked everything again and the bias resistor i was using for the push pull tube was 150k not 150 ohm…. oops. Now it works sweet. I think i still need to swap the output transformer but thats an easy job. Very loud for the size of it.

      Ill take a video or sound clip and post it up.

      Thanks for an awesome schematic! really happy with the amp!!!

      • Hi, sry for my late answer I was on vacation… I’m glad you found your mistake by yourself and I’m looking forward to your clip! 🙂

  63. Steve Swan Says:

    hi there, just a quick question from a newbie- i’ve been stuying loads of schematics online for a good first amp project and yours is the one i want to do but i don’t understand the schematic lines terminating in bold black blocks-are these just different forms of the triangles going to the earth/ground point on the chassis i’ve seen in other plans or is it just a symbol i haven’t come across yet? if anyone on the forum could answer i would be grateful!


  64. Steve Swan Says:

    izhak posted a question that answers my question i think- its the ground symbol, yay for me for figuring it out!

    ……. can someone still post to confirm it though :0)

  65. Izzy Madhatter Says:

    Hi, what operation class does the amp use? AB?

  66. Hi. I recently finished building this amp, and I must say, it’s quite loud, even with my bass.

    There are issues though. Whenever I use any of the controls, even on the bass, I get a very loud high pitch squealing sound. The volume/gain control doesn’t work at all, it’s always stuck on max.
    I would imagine the problem would be in the pre amp, of course. What should I be looking for?

  67. Steve Swan Says:

    does it matter what diodes i use for the PT gate? seen everything from 1A 30v to 600A 1000V!

  68. Steve Swan Says:

    on the schematic R34 has a value of 180, is that 180k? also c13 is a 2.2n. am i right in thinking its a 0.0022u? All the resistors i have ordered are all rated 200v or higher, is this right? sorry for the basic questions but all the parts come to £95 so far and i dont want to ruin the amp and waste time for the sake of £5 worth of components….

    • 180 means 180 ohms. Yes, 2.2nF are 0.0022uF and yes, 200V and higher rated components should be enough, especially in the power supply they should be rated higher than 200V, to be able to handle the given voltages and even higher voltages which will occur when you fire up the power supply without any load by accident or for testing…

      • Steve Swan Says:

        Thanks for answering my questions mate, I will post updates as and when I comlpete each section, I’m using this amp as a teaching tool for myself as well as a kit for a (hopefully) cool sounding amp! I won’t be building this quickly as I want to understand how each part of the amp works and how the components Work with each other and effect the signal chain- much better to do this hands on instead of reading theory texts!

      • Hi, If your stuck with understanding things, i found this website VERY helpful. Talks all about bias, push pull, class A, transformers and a whole lot of other stuff. Its written in plain english and done by Mesa Boogie, so its a reliable source. Good luck with your build! mine took a few days to work the kinks out but now it sounds awesome

      • Steve Swan Says:

        Me again! Is it better to keep all the resistors at .5w after the power supply or will the nice and cheap 1w with a few 2w metal films all be ok? not sure how the watt rating effects signal path as I’ve only just learnt ohms law while stuying triode and pentode theory!

      • You can use resistors with a higher power rating, too. They mostly just get bigger with higher ratings.

  69. Steve Swan Says:

    Cheers Hamo, read through the site and you were right, it was a helpful site! had a look at the lonestar amps too and they look good, might pinch some styling queues when i eventually make a cab! you should post a sound clip of your amp :0)

    • Ive been trying to get one, but the microphone on my laptop makes it sound horrible. It sounds like i have a phaser hooked up which is really weird. ill have to find a propper mic and try it out with that.

  70. Hi, would it cause any problems if i use a plastic enclosure and just use an aluminum plate as ground plane?

    Thanks in advance.

  71. Finally I finished the amp. It started with a hum but after putting in the resistors R13 and R16 is was quiet. It is quiet to me but my kids and wife are complaining about a high whistling tone. Even when the guitar is not plugged in. Is there a way to prevent the amplifier from oscillating?

    • The amp shouldn’t squeal, it is most likely a wiring issue. Try to make sure that no wires with the same signal phase are getting to close to each other (for example the input of the first preamp stage and the output of the second stage).

  72. Hi, I am going toi build this project, it’s my first tube circuit.
    only three questions:
    I’am receiving russian 6H2 and 6H6, i read that are similar in electrical parameters (but not same pinout), have you any recommendation for these tubes?
    In datasheet pin 9 seems to be a shield not connected to heaters, do I have to connect pin 9 to ground?
    Are you thinking about a simple powerful amplifier ?
    many thanks in advance and compliments for your very good project !

    • 1) Watch the pinout! 😉 The pinout differences are mainly in the heater wiring. In comparison to the ECC types It should be just breaking the connection between pin 4 and 5, connecting pin 9s connection to pin 5 and …

      2) Here Pin 9 is a screen between the two triodes and is usually connected to ground, yes.

      3) I have no need to, there are already a lot of simple powerful amplifier designs out there, that can be easily modified to taste. 🙂 (e.g. 5E3, 18Watt, Trainwreck, the AX84s types…)

      • Thanks for your alert, before starting to build it I revised all pin connections in order to adapt russian tubes. I finished to build it yesterday evening, I tested first heaters circuit and then I connected high voltage (one at a time) starting from the higher and so on, It was all good. I put in big electrolitics (industrial swithing capacitors) and a little discharge resistor to avoid shock. Only a defect, a little hum, this evening I’m going to check wiring and ground connections (shield connections too) and I will plug guitar to listen the sound.
        Next guitar (or hifi?) amp I will build will be a bit difficult, I am fashinated of GU-29 or GU-50 tubes.
        Many thanks, all and excuse for my english !
        regards, mauro07

  73. Revised/improved ground circuit (connected shield pin 9 of russian tubes 6H6 – 6H2 to ground ) and hum totally disappeared ! now I will set pot circuit in order to improve tonality of russian tubes (little close and dark, i think is possible to obtain more ampiltude of sound).

  74. hi, i’m wiring this amp and I’m thinking to add a 16 ohm output. I see you put pins 4-5 (pri 27k) to 4 ohm and 4-2 (pri 22,5) to 8 ohm. In your opinion is it possible to add 4-6 (pri 24k) to 16 ohm? in this way i will have 4-8-16 ohm output with common ground pin 4. What do you think?

    • I used 3&5 (17.6k) for 8 Ohms and 1&3 (15k) for 4 Ohms (see the schematic). The nearest would be 2&5 (15.5k) for 16Ohm, but you could try 3&6 (12.8k) to make switching easier or even use your pin and primary impedance suggestions (the bias would be a bit different).

  75. thanks a lot! I confuse miniamp and miniamp 2.0 output!

  76. guitar amp Says:

    Sorry for my English I am not good in it. I have a problem with the output transformer. Can I use this please?

    • Hi, this transformer has a primary impedance that is a bit to low (5.2kOhm). The transformer I’m using has a higher primary impedance of 17.6kOhm with 8Ohm secondary, which allows for a better bias point. To get the same results you should search for transformer that has a primary impedance of around 15-20k with the secondary speaker impedance of your choice.

  77. Hi, your amp sounds really thinking to build it…
    Could i ask you, with my bad english, about the speaker?
    In your demo are you sounding thrugh your amp fender speaker?

  78. Marcello Says:

    Thank you for your reply .. even the cabinet was made by you?

  79. mauro07 Says:

    Hi, I found a little mistake in preamp connection, now the volume is very powerful, only tone regulation is not working properly.
    I checked many times pot circuit and values, but I don’ t see the problem. I’m going to re-build tone circuit, may be a little bit different, then I’ll post you a video where you’ll hear russian tubes performances. Last evening I invited some friends to see it, they says it’s incredible a so little and simple amp can deliver this volume and quality of sound, even pot are not still working good. I tried two loudspeakers, a celestion 12GT75 16 ohms and an old 4 ohm Ciare bicone 10″ car speaker, they both work very well.

  80. hi. I,ve finished this amp! It’s great! I’m not good in electric but i’ve made a couple of mods.
    1) I added a volume controll with a stereo pot as in vox night train
    2) I’ve replaced v1 with an ecc82 for a bigger clean range

    thanks a lot!!

  81. Izzy Madhatter Says:

    Hi, after months (few time around the weekends) I have finished the amp. Unfortunately it oscillates (in high frequencies)! Can the problem be caused by too much anode voltage? Remember, I am the guy with the powert transformer that has 230V sec. instead of 200 (see above). I am asking this because this is the only part I modified.

  82. Hey i was just wondering if you have a bom, also where did you buy your parts and how much was the total cost. This build looks very nice.

  83. Most of the parts I ordered from and and the total costs where something a little less than 100€ I think. I’ll send a mail concerning the bom…

  84. Izzy Madhatter Says:

    Hi FcKw,
    Oscillating is gone after using shielded cable at some points. However, I did not do the coupling with R24.
    Now the anodes of the ECC99 are glowing! Remember, I am the guy with the 230V transformer.
    I think the bias is wrong?
    Above you say that the current through P2 is 46mA. Are you sure? This sounds a lot to me, since ECC99 has 5W Wa. So with the 235V anode voltage I calculate the maximum bias current (in mA) like this: 5 *1000 / 235 = 21, and I was told, one should stay below that, about 50 to 70 percent, this is between 10 and 14 mA. What do you think?

    • The case you’ve described won’t be reached because here Ia drops with Va rising to it’s maximum (power supply voltage on Ra). The limit you’ve calculated is the tubes limit if Va and Ia actually could reach those values at the same time. But you’re right if the anodes are glowing the bias seems to be to hot with your voltages, so you should increase the cathode bias resistor P2. Btw. it is 46mA for both triodes, as they are in parallel it is 23mA each. Here is a nice link where the basic behavior of a triode and its voltages is described:

  85. Chris Says:

    Realy neat job here!
    Im thinking about adding a headphone jack, do you think it is possible? and if yes whats your suggestions about?

    • It is possible, but I’d recommend a speaker simulation circuit to emulate the speaker response, because the guitar amps speaker response is a big part of the tube amps frequency response. Without this the overdriven amp will sound way to harsh and raspy.

  86. This is a great sounding amp, and I’m going to build one asap.

    Just one query, I simulated your circuit in LT Spice using the 150ohm cathode resistor in the o/p section as you mentioned. This gave 4.5W dissipation per triode for the ECC99. The spec sheet gives the max dissipation as 5W, which I assume means total dissipation for the tube; i.e. 2.5W per triode. I realise that the simulation probably won’t be 100% accurate, but this seems to be a very big discrepancy.

    Can you tell me what the voltage reading is across C18/P2?


    • Hey nice, I have a LT Spice model myself… 🙂 but I’m getting barely a Pa of less than 1.6W per triode with Va = 126V and Ia = 12.5mA. What are your measurements? Have you considered the OT?

  87. Sorry, now I’m confused. According to your schematic, the voltage at the centre-tap of the o/p transformer is 235V, so I don’t see how Va is going to be 126V. The resistance of the o/p transformer primary is about 150R, and the volts drop across it, if Va is 126V, would be 109V, giving a current through the transformer (and the valve) of 727mA. It would probably make a great room-heater, but the ECC99 and the transformer wouldn’t last very long!

    • I chose the OTs primary impedance with 17.6kOhm for an 8Ohm speaker (as noted in the schematic by the pin numbers). So 8.8kOhm on each anode. 109V/8.8kOhm = 12.39mA
      Here is a link to the datasheet:

      But I must have previously misread my notes, instead of ca. 25mA for each triode it meant ca. 25mA in total and so around 12,5mA each. I’ll check the real values when I can and will add a correction note to the previous comments… 🙂

  88. I think you’re confusing the AC impedance with the DC resistance. The DC resistance is what matters when the quiescent dissipation is being adjusted, that is, when you’re setting the bias. As I said before, the DC resistance of my 125C is roughly 150 ohms per half-winding. The AC impedance is important when the output load (speaker) is being matched to the valve output impedance. (N.B. It varies in proprtion to the frequency.) It doesn’t matter in terms of the DC conditions.

    I’ve just rechecked my Mini Amp 2.0 simulation and to get 2.25W per triode (I don’t go to the maximum dissipation when I’m building an amp.), requires a cathode resistance of 420 ohms, giving a current of just under 10mA per triode multiplied by the voltage drop across each triode (234.5V [Va] – 8.38V [Vk]=226.12V), gives 2.26W per triode; 4.52W in total, just under the maximum of 5W.

    I don’t expect the simulation voltages to be exact, but they will be a good starting-point when I set up a real Mini Amp 2.0.

    I hope this is clear to you. If you like, I could send you the LT Spice files for the Mini Amp 2.0 so that you can run your own simulation, which might help clarify what I’m trying to explain. I seem to recall that you’re familiar with Merlin Blencoe’s work. He gives a pretty good explanation of all this; better than I could give.



    • I should perhaps add that I don’t know whether the 5W maximum dissipation refers to each triode or the whole valve. The only data sheet I can find doesn’t make that clear. I was hoping you might be able to clarify that point.

    • It is 5W maximum dissipation for each triodes anode. Yes, there is a difference between impedance and resistance, but it is the impedance of the OT the tube sees as load at the anode and it is the impedance your using to draw the load line to set the bias.
      I’ll remeasure the amps output stage when I have the opportunity to and compare them to my spice model to clear things up. I mainly used the spice simulation to get rid of some distortion artifacts from the cathodyne PI and for visualizing the frequency response, but I think I never really checked if the simulated power amp section meets the measurements of the original amplifier. I’ll send you an email so we can exchange our spice models. Cheers.

  89. Excellent. Thanks.

    I’ve bought a couple of ECC99s, and I tried one in a mini Trainwreck type amp that I built, originally fitted with a 12AU7. What a difference!

    I’ll look forward to hearing from you.


  90. Great amp!
    I was wondering if some one already created a nice turret board for this beauty.

  91. Hello

    I am nearly finished building this amp – with the Russian valve instead of the ECC99. I have managed to get it into a smaller box – not by design – I just bought the wrong one. It all fits if a little snug. I have put the large caps underneath a tag board on which I have put most of the other components. I’ll send some sound samples when finished, and if anyone want a photo of the tagboard layout with all the connections I’ll gladly pass it on. Great job.

  92. Still on the bench, and my intention is to built a “tiny” combo. Until now I m facing 2 issues.
    The first looks like a ground prob that I cant still figure out (though is gone away when I connect the ground of Line In –see below-), and second is that my PT runs really hot. (defective or what?)

    As for the mods:
    1)I added Night Trains master volume and works fine.
    2) added a Line In/Out after C13 wich seems to work well (though overall volume drops and final sound goes like a totally clean amp).
    3) Headphones jack installed with a 10 Ohm/5W resistor paralleled with a 33uF cap and an 100 Ohm resistor to the tips. Im not a guitarist but just a hobbyist and to my ears the outcome sounds decent enough.

    As for the transformer im using this one with an 270 Ohm resistor in place of R34. Voltages are 279-231-217-209.

    Keep up the nice work,

  93. This is great sounding amp and it’s on my top wish list now!
    I like to recycle my Firefly 1W amp which has Hammond 269EX (380V C.T.@71ma, 6.3V@2.5A) to build your miniamp 2.0.
    I wonder if I can use the Hammond power tranny without any change?

  94. Final report. Now everything is working perfectly. The PT was faulty and immedietly responded and sent me another one.

    I assembled all in a small wooden “cab” as a tiny combo (a bit inspired by Fender Champion 600) with a 15W 6.5inch speaker made in Czechoslovakia (!). As expected it is realy getting hot after an hour or so due to poor ventilation and proximities with tubes, transformer and speaker’s magnet. For that reason i installed a pc fan wich do the job but i realy dont know for how long the capacitors inside will survive.

    If i only can suggest one thing. The bass pot by my opinion and taste has to be replaced with a log 500k or a 250k linear to work more smoothly.

    Thank’s for the inspiration

    • Good to hear that you got your PT problems solved. I have to try your simple headphone approach, I tried it once with a speaker emulation circuit, but that wasn’t really getting rid of the all the unpleasant distortion artifacts you are getting without the speakers frequency responce while overdriving the amp. You are right, the bass pot could be a little bit more balanced over its full range, I’ll definitely try out your suggestions on this some day. Are there any pictures of your build, I would be very interested to see your tiny combo. 🙂

      • As for pics if not tomorrow, most possible after a week or so.
        And a 250mA slo-blo fuse on mains works fine. An 1A i think is for builds of 50-60Watts (but not so sure as im realy a novice) .

  95. And the pics:

  96. Hello. I have now finished the amp, but the sound is very harsh. I have checked the wiring many times, and I am using the russian valve in place of the ecc99, and either 12ax – at or au 7s for the other 2. I am however about 10 volts short on all of the test points – could this be the problem?

    • I think I have found the answer – don’t use a squiier strat. I’ve tried it with my acoustic, which always sounds horrible with its undersaddle pickup, and it sounds great. A little more work and I’ll post some samples

      • The voltages shouldn’t be a problem. Does it also sound harsh with the treble turned down a little? The highs can be really pronounced with the treble all the way up, which is a really nice thing to make humbuckers chime, but with singlecoils it is nicer to have the treble rolled back a bit… What speaker are you using?

  97. Now got a humbucker playing through it with a 12″ clelestion speaker. Sound is great. You are right about treble, it almost acts like a gain pot. A little hum to sort out, but I’m having too much fun with it to take it apart again at the moment.

  98. Here is the sample

  99. Man this is awesome!!!
    Can U please add tubes pinout numbers.

    Thank U

    • I used a12at7 for V1, a phillips equivalent of 12au7 (Jan5963) for V2, and a Russian 6N6P for V3. The main difference in the pinouts is that the European valves have the heaters wired in series with the mid point at pin 9, so you effectively wire them in parallel by linking out pins 4 and 5 and feeding the heater voltage to pins 4 and 9, whereas the Russian valves have the heaters in parallel across pins 4 and 5 so you wire the voltage to pins 4 and 5. Then you must wire pin 9 to ground. Otherwise the pinouts are the same 1 anode, 2 grid, 3 cathode for triode one and 6 anode, 7 grid, 8 cathode for triode 2. Am now building into a bigger cabinet as mine is too small. The guitar incidentally is a first act CE540 I picked up for just over 100 quid. If you ever see one…..

      • Thanks man 🙂

        One more question… since i can easily find 12BH7, can i use it instead of ECC99?

  100. This is where my expertise leaves me, but the 12BH7 is a replacement for the 12AX7 and could possibly be used there, but not instead of the ECC99 (it is a different size (height)and draws less heater current). I have put one of these valve in the ECC99 position when fiddling around, and they just give a very dirty overloaded sound. The Russian ECC99s are readily available on Ebay for just a few pounds

    • Thank U again

      Would it be helpful for more noise reduction to add bridge rectifier to PT 6.3V and then to tube heaters?

  101. Just wondering if I could get a copy of the BOM. Thanks

  102. dear sir :

    I want try to diy The MiniAmp 2.0, I have 2 question
    1)what is hammond125 B? is transformer?? what is 1 3 5?

    2) all the rsistor use the 1/4 wattage ok??  

    sory my english is bad ,and thx your answer

  103. the hammond 125b is transformer ,can you tell me input /output Voltage??( 1.3.5 Voltage)

  104. What’s the minimum voltage ratings required for C11, C12, C13, C15, C16, C17? I purchased capacitors rated for 100V for C11 & C12, and capacitors rated for 50V for C13, C15, C16, & C17. However, I’m thinking I should have purchased ones with high ratings.

  105. It’s awesome to pay a visit this site and reading the views of all friends about this post, while I am also zealous of getting experience.

  106. Hi Friend

    I love your amp ….i want to build one!

    I already build some pedals a small amp with a 12au7 as pre but i want something like this beauty.

    Can i use an Hammond 125A? instead of the B?
    I have one here that a friend gave it to me….

    • Unfortunately the 125A won’t stand the output stages bias current.

      • Hi, earlier schematics show you using the 125A and I think the Firefly also used the 125A… why are you saying it doesn’t have enough current for this circuit now? Thanks!

      • Hi Derrick,

        that is because this amp uses a push pull power amp configuration with a phase inverter that produces more power than the self-split power amp configuration the other circuits are using.

  107. Hi,

    I recently build the amp and are struggling to get it to sound nicely.
    It has decent clean tones but overdriven it sounds terrible to me.

    It’s built pretty much according your schematics with the following changes:

    – ECC82 instead of ECC83 for first tube.
    – 250k Bass pot instead of 1M.
    – Master volume implemented as in Vox night train.

    I’m using a ibanez with active humbuckers to play with.

    Instead of trying to describe what i mean by “terrible” sounding i uploaded a video so you can hear for yourself.

    I’m kind of stuck finding the cause of this noise so it would be great if someone with more experience may be able to help me understand what could be the problem.

    Thanks for a fun project!


    • Realised just now that clicking on my name should take you to the videoclip. (I thought the clip would end up being embedded in my post)..


    • An update testing today.

      Putting ECC81 in V1 and ECC82 in V2 made the amp sound much better and without the horrible overdrive. Also this seems to be the only combination of ECC81,82 or 83 in V1 and V2 that produces good sound.

      The ECC82 has only 19 as gain factor where ECC83 has 100 and ECC82 has 60. So lowering the gain significantly on V2 seems to help.

      What could cause this beahavior?

      Thanks for any ideas 🙂


  108. Can i ask you Send/post your important voltages so i have something i Can compare When measuring mine.

    • A=237,B=216,C=210,D=205.
      With ECC83 in V1 and V2 my Anode voltages are.
      V1a = 97V, V1b=97V, V2a=185V, V2b=166V.


    • Yes, I’ll measure them for you when I find some time. What are your voltages on the cathodes?

      • Cathodes:
        V1a = V1b = 0,76V. V2a=0,96V. V2b=51V. V3=6,8V

      • These voltages don’t look to bad… Compared to my spice simulation just the values of the 3rd triode stage seem to be a bit off, there the simulation has: Cathode: 2.97V; Anode: 133.6V Perhaps you could check this stage again, but I’ll have to recheck the values by measuring my amp…

      • Resoldered the third gain stage and measured again. This time i got Anode = 140V, Cathode=2.1V, Grid=1,6V. Closer to your spice values but it sounds still as bad as before.

  109. Should the volume and tone stack pots be audio or linear taper? Thanks

  110. I am really grateful to the owner of this web site who has shared this great article at at this time.

  111. Charles Wahl Says:

    Hi there FcKw — what a great sounding amp! I had planned to build Doug Hammond’s Firefly, but the over-gain of cascode and the self-split output stage are giving me second thoughts — D. Hammond has himself evolved the design to PI > ECC99. I’d like to try your design instead, which seems to have a wide “clean” to “hairy” envelope.

    Problem: I’m in USA, so at the mercy of 117 VAC. I already bought a Hammond PT, 369EX, but it may be too powerful:
    VA=45 / Secondary AC 380 V (center-tapped, 190 V each side) @ 75 mA / Filament 6.3 V, 2.5A

    The Hammond 363AX mentioned above has 200 V secondary (also CT), but Filament is only 5V, according to their website.

    The Hammond 369AX has 250 V secondary with 6.3 V Filament.

    If you could provide some guidance about how I could adapt the 369EX, or else the 369AX, I’d greatly appreciate it — I’m an electronics noob, unfortunately, especially where the complexities of tube-amp design are concerned.

    • As the 369EX provides to much secondary voltage and the 363AX to low filament voltage, you should use the 369AX with a center tapped rectifier design. See the firefly schematic for the differences in the rectifier wiring, there both versions are shown:

      • Charles Wahl Says:

        I’m pretty familiar with the Firefly schematic and the center tapped configuration. What I’m perplexed about is how to get the same voltages (and capacitances, if that’s an issue) as you have on your schematic, using a transformer like the 369AX, having higher secondary voltage. On the Firefly schematic, B+ voltages are 265, 219, 210, while yours are 235, 211, 203, 199. Any advice about how to handle that?

      • Don’t mind the slightly higher voltages, it will give you just a bit more clean headroom. All I would do is rebias the ECC99 with a marginal higher cathode resistor.

  112. Charles Wahl Says:

    OK, great. I’ve never done it, but I imagine that by reading up on Aiken and Blencowe websites I can figure out how to tweak the cathode bias resistor. Maybe starting with a variable resistor as shown on your schematic is the best way.

    Just so I understand completely: you feel that I could stick with the power section resistors and filter caps as shown on your schematics (that is, everything downstream of the rectifier bridge) and things will prob. work out OK?
    Thanks for your help,

  113. Charles Wahl Says:

    Oops! One more question, regarding the PT: if you had the choice between the Hammond 125B (9 henry primary inductance) and this one by Musical Power Supplies (the OT5PP with 5W rating, 30 henry inductance, but limited apparently to 22.5K ohms primary),
    would you still advise using the 125B? I’ve got one of the OT5PPs, which got good reviews from a lot of the people subbing it for use on D. Hammond’s Firefly — better bass output. I realize that this would affect biasing of V3.

  114. Charles Wahl Says:

    OK, thanks very much for your help.

  115. I am really impressed with your amp knowledge and this project. Do you know if any one ever worked out a turret board layout?

    • Not that I know of, you would be the first! 😀

      • David Says:

        I tried to do a turret board on my first build, but the problems are that the board takes up a lot of space, and the extra interconnecting wires also are a nuisance. If you want to do a turret board – which of course can make for a much neater build – then consider a much bigger enclosure.

  116. Been meaning to send this for a while.
    I finished my build a few months ago based on your design but with a few small mods. The mods were not for any improvement in design, I just had a different purpose. I had bought a Vox Pathfinder 10 for $80 and used its cabinet, chassis and speaker because there was no way I could build one as cheaply as that. The mods were… A Master Volume, two-way Tone Stack and a feedback switch. These mods were made so that I could use the existing faceplate of the amp. I also took a voltage divider feed from the speaker output to feed the line-out/headphone socket in case it was ever needed. I ended up using a 12AT7 and a 12AX7 for my driver tubes because I wanted a cleaner sound at upper volumes for the jazzy stuff I play. The ECC82 gives a pleasantly full sound out of the little 5″ speaker, noticeably better than a 12AU7. The result? A fantastic little practice/bedroom amp that gets a flogging almost every day. Thanks for the inspiration man!

  117. Oops. Meant to say that I used an ECC99 in the output, not ECC82.

  118. Charles Wahl Says:

    FcKw, I’m trying to figure out how you’ve biased the ECC99 relative to max. plate dissipation, and the discussion you had with John on 11 July 2012 wasn’t really concluded. I haven’t used Spice, but have done a load line diagram on the plate curves, per Merlin Blencowe’s Push-Pull chapter (Valve Wizard). If you don’t mind taking a look at it, I would appreciate it. Could you send your email address to, so I can forward it?

  119. Hello, I want know if I can use any suitable tube for ECC99 like 12AT7, 12AU7 , 12DW7 or ECC88/E88CC, or russian 6N2P-EV or 6N1P. Thanks

  120. Hello, I build the mini amp in a army look, inside a ammo case.
    Added a master volume and a EM80 VU indicator.


  121. Second attemp :o)

  122. And finaly some sound clips.

  123. I notice some people having trouble whit high B+, i used this schematic, worked fine for me.

  124. FcKw,
    Thanks for the schematic and your’e enthusiastic comments!
    I build the amp for a friend, and he loves it!!

  125. Looks awesome, i might give it a shot later on 🙂 however, i wondered if you could do something similar but for bass guitar. in advance, thanks for zour reply 🙂 Greetings Izzy

    • You could use it for bass, but you would have to adjust the filter sections to let more bass through. And as basses a need a bit more power to reach the same volume, I would recommend to upgrade the power amp section to 15Watt or so.

      • Thanks for the reply 🙂 changing the filters would mean changing the capacitors right? what values would you recommend? and how does one beef up the power amp section? sorry i’m quite new to this. Greetings Izzy

      • I have no experiences building bass amplifiers put raising the cathode bypass caps and the coupling caps between the stages should raise the bass response. To get 15watt out of the power amp you would have to change to an EL84 or 6V6 configuration with a bigger power transformer, like it is used in the Vox Night Train for example.

  126. Great Project!
    But..I got a question regarding the Pots. Are those all linear or are some of them log pots? Thanks for helpin out

  127. Volume pot is audio taper, the others are liniar.
    I have had a lot of fun building this perfect little amp. 🙂

  128. I found this toriod power transformer on the amp maker web site is this a possible candidate?
    There is another larger one on the power transformer index page.
    This output transformer might make a good choice. Any thoughts?
    Sorry just starting this journey and need to source out the parts first. I don’t mind using local sources either but the OT primary impedance seems high at 15 – 17.6k Ohms. So using a OT for a Fender or Marshall won’t work.

  129. agung mahendra Says:

    Hi, i want to bulid this amp with custom OT , but i am little confused with OT transformer spec . whether this picture is correct?

  130. Izzy Madhatter Says:


    I would like to add a master volume, but I am a bit unsure how to do that exactly. A first approach made the power tube anodes glow and sounded weak. Can anyone post the detail from a successful approach?
    The night train uses four caps after PI before MV and the values of the grid resistors of the power tube are different. Any more details/clarity welcome!

    Thanks, Izzy

  131. Hello! Can I ask you for BOM please? Any chance anyone can post schematics with master volume? I found the mentioned night train schematics, but no idea how to implement MV to your schematics. Thank you in advance!

  132. mrsmash,
    Take a look at the link just above you’re post 🙂
    Not hard to implement, add the parts as mentioned in the box
    (Added Parts) just after the both 100n caps, works fine in my build.
    Just click on the ammo box above 🙂

  133. Izzy Madhatter Says:

    Awesome, thanks a lot! Next mod: a buffered fx loop would be great. Has anyone a good approach for this?

    Thanks, Izzy

  134. Sorry no FX loop on mine, but the EM-80 is also a cool add-on 🙂

    • David garcía Says:

      Hi Rinus, I have one EM80 for this project, but your power transfo is the same 30Va ?
      The flament current of the four tubes exceed the 1,5A .
      Thanks too FcKw for share this project

  135. Hey David, forgot to mention but i used a slightley bigger one good thing you noticed!

    • David garcía Says:

      Ok, thanks.
      A slightly greater Transfo usually means higher voltage in the secondary ( + 50v) . you correct the power supply or did you use the same schematic?

  136. Hey David, take a look at my post of oktober 7.

  137. Hi David, i took the ground from diode 3 and 4 as “center tap” so it is mounted between diode 3 and 4 and ground.

  138. I made a card for my construction of this MINIAMP 2. For those interested can find the photos posted on my Facebook profile.

  139. Salvatore, did you make a PCB for the amp?
    I can’t find it on you’re FB.

  140. Job well done David, i’m impressed.
    And you kept it real small, a new MiniAmp is born. 🙂

    And again, a big hand for the creator of this nice peace of Art.
    Thank You, FcKw !!!

  141. That would be nice Salvatore,thanx!

  142. Hey !
    There seems a big interest in the PPIMV. I don’t know where to place it. It should be just a dual pot (500k) diret after c16 and c17, am i right? would this dual pot replace then replace r30 and r31? (what are they used for anyway?)
    thanks and cheers. i’ve been looking at this project quite a long time and i love it.
    Supergeil 🙂

  143. plis Salvatore the pcb!!! 😀

    • Hey Rinus,

      I’ve already seen this image above. But i don’t get what R30 and R31 are used for. Could you explain it to me? Is it like i thought it would be? The dual pot replaces those two resistors?
      Maybe you could show me how you did it?

      Thanks! 🙂

  144. Rinus , you have the PCB ?

  145. Julez, R30 and R31 are part of the bias circuit, do not remove them.
    Just add the 500k dual log potmeter and the two 1uF capacitors.
    B.t.w. Salvatore has developed a nice circuit board, whats making building this amp a easy job, if you know what you’re doing!
    But be very carefull if you never had somthing like this on hand, the high voltages that are present in the cicuit can kill you!!

    • Hi Rinus.

      Thanks for your information! I thought the variable poti P2 is the only part for biasing?
      But now it makes sense. I just would like to know the theory behind those two resistors 🙂

    • A PPIMV info I found on the Metropoulos amp forum while ago says,

      “This mod involves removing the two 220K bias-feed resistors on the board. The 2M2 resistors must be installed between the centre lugs (to grids) and the left lugs (from bias supply). The resistors make the pot = 220k when dimed – which means this PPIMV should sound the same when the amp is dimed as if you didn’t have a master at all!”

      And the R30(220k) and R31(220k) seem to be the bias feed resistors. Aren’t they?

      reference URLs:

  146. Some time ago i discovered this OT, could be interesting for this project, did anybody used it already?

  147. Julez, you can find a lot of information on the tech pages at Aiken Amps.
    And also,

    The’re is a lot of info on the internet, that’s were i have learned a lot about tube stuff. 🙂

    • Hi, I have just ordered the transformers for this great little amp. I ordered the stock PT but went with the OT5PP OT from Musical Power Supplies. I just wanted to give a heads up that they now are offering an OT5PP+ that features a 1 inch thick laminate stack (a 20% thicker core) that gives better low end. Costing US$32, they are currently being wound to order, feature a 22k5 ohm primary, 4, 8 & 16 ohm secondry taps & the windings are interleaved. I was told to allow 10 days from receipt of payment (PayPal) til shipping. I will get some pics posted when complete. Thanks for sharing this great design. Cheers

  148. Hi, very nice project.
    I’m going to build miniamp 2.0.
    Salvatore, can you send the layout?

  149. Hello! Do you think replacing solid state rectifier with tube one would make the amp sound even better?
    My thoughts -> Maybe EZ81 / 6CA4 rectifier tube(because of 6,3V filaments, If=1A) – so maybe changing toroidal 30VA PT to same type with higher rating, then changing capacitors and resistors somehow in power section to match the needed voltages on A,B,C and D.
    Would it be easy to figure it out?

    Datasheet for JJ EZ81:

    • Adding a tube rectifier would be pointless. That a lot of work and trouble for no gain. If you want “sag” you already have it with R34 (180 ohms). It does the same thing and is much cheaper.

  150. Probably last mod I’m thinking about before starting build -> FX loop. I found schematics from Weber website. Do you think I can insert it directly without any other changes into MiniAmp schematics as show with blue spot. Or another spot between 3rd gain-stage and phase inverter?

  151. tntptp Says:

    Hi, very awesome project. I have been looking for a good transformer to use and found the PT190.2 from Musical Power Supplies, which states 190-0-55-190V and 120mA. For filament outputs it has 6.3V and 3A. Will this work for this project? The schematic states “200V”, so this one is slightly low but has enough amperage. Any feedback would be greatly appreciated. I’m just getting started on buying parts. Thanks!

    • ivan H Says:

      Hi tntptp,
      the transformer u mention has a center tapped secondry so would require that u use a full wave rectifier rather than the bridge rectifier shown in the schematic. Both the HT & heater winding supply plenty of current, u’d have no problem adding another output &/or pre amp tube to the circuit using it. Just FWIW, I ordered the stock PT from tubetown & had it shipped via the normal mail service to me here in Australia. Delivery cost was about AU$6-50 & I received it in just over a week from the time of making payment. Hopefully my OT5PP plus from musical power supplies arrives in the next day or 2 so I can get started on. I intend folding up a chassis & have some G10 & turrets so will do a turret board for it. I’ll try & get some pics up when done.

  152. tntptp Says:

    Hey Ivan, thanks for the reply. Actually your the one that gave me the idea to try Musical Power Supplies from an earlier post. I’m getting the OT5PP+ along with the PT190.2. Regarding the PT190.2, I do understand what your saying, that I need to use full wave rectifier (two diodes). The two diodes would then tie to R34. What I’m having difficulty with is understanding how this provides 235V at point A? Do you think it’s better to order the original PT?

    • ivan H Says:

      Hi tntptp,

      • ivan H Says:

        Hi tntptp,
        accidentally posted that last post too early. Notice that transformers HT secondry is 190-0-190, so the whole winding is 380 with a center tap. If u search the web u will find numerous sites that explain in depth the theory of rectifiers ect, that should clear things up for u. As to which PT to use, IMO the one from musical power supplies that u indicated would be fine, & if u plan on adding a tube or two for any reason, will supply the necessary heater & HT current. If on the other hand u wish to build the amp as shown in the schematic, I personally think its best to use the PT the amp was designed around, tho that’s just my opinion. Oh, the OT5PP + actually has a 25% thicker core than the OT5PP, not 20% as I stated in an earlier post. Hope this all helps.

  153. To tntptp: What you can do is wire your PT the same way as on the following schematic from another tube amp:

    The principle is exactly the same (forget about the voltage values shown on this schematic, the PT rate is different). You’ll get a little lower than 235V because your windings are 190V instead of 200V, but that should not matter. You could also lower a bit the value of R34 if your DC voltage is way under 235V, but I doubt you’ll need to do this.

    The difference between the original 200VAC (one winding) and the 2x190VAC PT your are considering is that, in the first case, a bridge rectifier is used. In your case, you’ll use a two-diode rectifier (or four as in the schematic above because they are paired in series, but that does not make much diffference).
    Hope that helps.

  154. tntptp Says:

    Duke – thanks for confirming this PT will work in the 2 diode rectifier configuration. I think I am going to try this PT along with the OT5PP+ from the same manufacturer. Next step is to finish my parts list and buy everything.
    thanks again!

  155. Has anyone got Salvadore’s layout? Can we PM from this blog?

  156. IvanPerks Says:

    Can someone send me Salvadore’s layout too please?

  157. […] for the fun of it. After a little looking around I found this little amp that looks like a blast. The MiniAmp 2.0 | DIY Guitar Freak I even picked up a few '50s tube powered TV boosters to use for a head cab & chassis. I'm not […]

  158. Hi man, Amp looks great. I’m going to give it a go myself. I’ve done loads of vehicle wiring – including making my own looms for engine conversions etc. But very little to do with DIY curcuits. I understand the risk of high voltage DC 🙂

    I have a few questions.

    The bridge rectifier – What Diodes have you used?

    Is their any movement in input voltage (200v) + and – before things start to go wrong? (struggling to find a transformer)

    Did you ever get around to doing the parts list?
    I’ve done one myself. But not knowing alot about capacitors – what voltages are your’s rated at?

    Cheers Joe

    • Hello Joe!

      Ad diodes) 1N4007 will work fine.

      Ad transformer) If you live in Europe, Tube-Town eshop got most of the parts including PT, link is in description. If you find PT with higher primary voltage you can lower it to +/- 200V using diode+transistor (Search for “high B+” in this discussion and you find Rinus link).

      Ad voltage rating for caps) I simply used all with 350V+ rating, but I am noob 🙂 If you read through whole discussion you will find out exactly which one’s are high voltage ones (every one in power section, those in path of B+’s, coupling caps and some others… ). Watch out for power rating of resistors too.

      I can send you 2 layouts from guys in here if you write me email (mrsmash23 at gm4il d0t c0m) for inspiration (you can see voltage lowering circuit in one of them if needed).


  159. stephane Says:

    hi nice sound for this amp i’ll make me one.

    i saw somme people have making a PCB, anyone has the plan ?

    best regards


  160. Hi, yes I can send you the PCB layout and pdf files that I got from someone else. Juste post your mail adress here.

  161. ok, ça part à l’instant même. Dis-moi si tu as tout reçu (quatre fichiers). Vérifie ta boîte spams si tu reçois pas.

  162. Juozasu Says:

    Good Job. But No Mastervolume = no drive at low volume levels.

    Also at full gain/volume here – the power amp stage goes to overdrive.

  163. Trying to post pictures of my newly built MiniAmp 2.0.


  164. Another attempt:


    • Stéphane Says:

      vert good job nos we want to have a YouTube démo 🙂

      superbe tu vas pouvoir me filer des conseil. tu as pris une quoi alim principal ?

      tu as quoi comme bouton du coup? et en face arrière c est quoi le switch?

  165. Merci ! Schéma standard. Tous les boutons standard (les libellés sont masqués, faut que je refasse la face avant). Alim identique à l’origine (transfo torique tube-town), switch d’impédance à l’arrière pour basculer entre 4 et 8 ohms comme sur le schéma.

    Sais-tu comment on insère des liens ou des images dans ce blog ?

  166. Again, trying to post links to pictures of my newly built MiniAmp 2.0:

    • Hello. From your picture looks like you mounted a protection
      resistor across the output pin and the ground to provide a load
      in case you switch on the amp by mistake without a speaker connected. What is its value ?

      • Hi Joe,
        Yes, good catch. I used a 10 ohm 2 watt resistor. That’s more than enough to protect things in case of error.

  167. Can someone send me Salvadore’s layout and BOM, please?

    sngkm at yahoo dot com


  168. Hi,
    Check you mailbox. 😉

  169. Really appreciate for this training TIPS. In young age every one is interested in playing rocking musical instruments like guitar, drums or piano.

  170. Hello,

    Can someone send me Salvadore’s layout and BOM, please?

    taomk2 at live dot fr

    Thanks a lot !

  171. On there way, Eric

  172. Hi, I built my version of the mini amp about 2 months ago. My girl recently gave birth to my son & as she lives quite some distance from me the amp hasn’t had much use. It differs quite a bit from the stock version. I had planned on doing a turret board build, but I found an old 10 watt transistor amp that I gutted to use the chassis. A turret board would not fit in this so I used double sided tag strip to mount the bulk of the components, with some mounted either between the tag strip & the tube sockets or directly to the sockets. The B+ line has 100uf after the rectifier, then the 180 ohm resistor & 22uf as the main filter for the OT/ECC99 plates. From there the B+ line is stock except each electrolytic is bypassed with a 0.01uf/630V polyester. I used 2 inputs set up in the very common Hi/Lo fashion viaa switched jack

  173. Hi, glad to see this amp is still being built. I also buit mine about two months ago. See the orange thing above for pictures.
    How about some pictures of yours Ivan? Also, how does it sound and what is your bias point for the output tube? Mine is really hot with about 22mA per side (I use separate cathode resistors). But I like it this way. My B+ at OT center point is 223V. That’s 219V at plates.
    I am now planning on a post-PI MV and/or some output attenuation.

    • Hi Duke, at the moment I have both ECC99 connected to a single 150 ohm resistor & 220uf electrolytic. The voltage drop across the resistor is 7.05V quiescent, giving a shared bias current of 47mA, or 23.5 per triode. There has been no indication of red playing from no signal thru to fully cranked so even tho it is biased quite hot the ECC99 seems able to cope with it. The amp is mid/upper mid heavy, having no treble peaking in the circuit. Playing my Stratocaster with custom shop Texas specials thru it on the bridge pickup, the treble is not excessive & doesn’t need to be rolled back, & it really grinds. Using the Hi input with the master up, it doesn’t clean up with the guitar volume easily, requiring the gain to be well down to achieve this. Rolling back the master a bit alleviates this, tho the guitar volume still needs to be quite lo. Plugging into the Lo input helps. Plugging in a LP, master on 7 or 8, gain on 7 & the bass on 2, push the mid & treble & using the bridge PU gives a great, really overdriven tone that I love. Pushing the gain drives it a good bit harder but I prefer it around 7. My wall voltage fluctuates quite a bit at times, between 240 to near 250VAC. At the moment its off peak demand so its high. Heaters are showing 6.7VAC. DC voltages are 263 at the rectifier, 253 at the OT center tap, 225, 216 & 211VDC at successive nodes. Plate voltages (from 1st gain stage thru to output plates) are as follows; 152, 129, 144, 183 & output plates are 241VDC. I know these are a little high but this is with the wall voltage high enough that the heaters read 6.7VAC & should drop a little when demand is higher & supply is closer to 240VAC. I’m looking forward to tweaking it now. I’ll try & get some pics up. Cheers

      • Hi Ivan, thanks for the details. Your bias point is about as hot as mine. Though it seems to work “as designed”, still it’s pretty hot as compared to other ECC99 PP designs that can be found here and there. Have a look at tube-town low wattage kits and you’ll see they use one 330R when we use a 150R. Never mind, I like it this way and I don’t see any red plating either.
        I’ll have to rewire my PT primary and use the 230V tap instead of 240, as my nodes and plates are pretty low.
        My B+ nodes are, from A to B, 223, 199, 191, and 186.
        My plate voltages, from PI back to preamp, are 159, 121, 72, and 78V.
        Wall voltage was 238V when I took these measurements. So I might give a try to the 230V tap in order to get more headroom.

      • Hi Duke, I like the ECC99 biased hot like this too. For the NFB/presence I’m thinking to take it off the 8 ohm tap, use something like 27k in series with a 50k Linear pot & apply it to the cathode of the gain stage preceeding the PI, then experiment to find my prefered feedback resistance value & slot it in. For the presence I’ll use the typical 5k/0.1uf. I’ll get back to on results. Cheers

  174. Hi, I completed my version of the mini amp about 2 months ago however my girl recently gave birth to my son & as she lives quite a distance from my home, I haven’t spent much time with my guitars & amps. I had intended a turret board type build but found an unworking 10 watt transistor amp that was an ideal platform but was too small to allow for a turret board. I used double sided tag strip to mount the bulk of components, with the rest mounted either between the tag strip & tube sockets or directly on the sockets. The pre amp differs quite a bit from stock. I used 2 inputs set up in the common Hi/Lo fashion via switching jack sockets, a 1 meg & two 68k resistors. The 1st gain stage uses a 2k7/.68uf cathode combination & 100k plate load. The second gain stage is stock except for a 100k plate load. The third stage uses a 1k5/10uf cathode combination (the 2k7 to ground is omitted & no NFB is used around the pre amp/tone stack. The tone stack comprises a 500pf treble cap & 47k slope resistor, tho I may experiment with the slope resistor for a little less miss. All coupling caps are 0.022uf/630V polyester, except for two 0.1uf caps between the PPIMV & output tubes. I also omitted the 1 meg grid leak on the 2nd stage, using just the 1 meg pot for this. I also changed the B+ line slightly with 100uf at the rectifier output, then the 180 ohm resistor & 22uf for the ECC99 plates. All electrolytic are bypassed with a 0.01uf/630V polyester cap. I used a single ground buss that is attached to the chassis at the inputs. Each stage’s filter is mounted under the tag strip in the appropriate place. Even with no under chassis shield fitted, the amp is pretty quiet. Plugged into my 1960A 4×12 loaded with 2 greenbacks & 2 vintage 30’s & with the PPIMV & volume cranked this little beast is much louder than I expected & really overdrives a lot. This suits me fine as I don’t play clean all that much. I’m looking forward to spending time playing this little amp & tweaking it a little. I’m thinking to maybe incorporate a NFB loop with presence control around the output stage & PI, something like was used in Fender 5E4-A or 5F4 super amps. We’ll see. Cheers

  175. Hi, I didn’t realize that 1st attempted posing had up loaded so redid it, sorry. I’m posting via a phone that has been dropped too many times so black’s out. I’m pretty well computer illiterate but I’ll see about getting a couple of pics up. Cheers

  176. noise-canceling Headphones

    The MiniAmp 2.0 | DIY Guitar Freak

  177. Hi everyone, so I have successfully fitted my modified mini amp 2 with a NFB loop around the output stage & PI, incorporating a presence control. With only a little playing time on it I am happy with the outcome. With the PPIMV on 6 the presence control is quite active (these type master’s defeat the effect of NFB as they are turned down), giving the amp a bright, shimmery tone when the presence is up. The feedback is taken off the 4 ohm tap of the OT5PP Plus OT. The feedback resistor is a 56k & is applied to the cathode of the stage preceeding the PI. The cathode has an unbypassed 1k5 resistor to ground. The presence control is made up of a 5k Lin pot & a 0.1uf/100v polypropylene cap that is paralleled with the 1k5 cathode resistor. For anyone wanting to try this using the same OT, I will describe the OT primary & PI connections so that the amp will take negative, not positive feedback. I have the signal taken from the CATHODE of the PI & the OT’s BROWN primary lead connected to one triode of the ECC99, & the signal taken from the PLATE of the PI & the OT’s BLUE primary lead connected to the other triode of the ECC99. The presence control is grounded at the same place on the ground bus as the 1k5 cathode resistor that it is paralleled with, to avoid ground loop hum. Hopefully some may find this useful. Cheers

  178. Hi all,
    This projects looks like it rocks. I’ve been able to find the transformers but could someone possibly send me the PCB layout talked about above and any parts lists that have been complied?

    thanks a bunch!

    guitarplaya1423 at gmail

  179. I’m in the process of building a low-power amp, and I came across this design. I was going to build a dragonfly, but this looks better. The problem is that I already built the power supply for the dragonfly. It only has three different B+ voltages, while this design has four.

    Can I use the power supply I already built? If so, which two points can share a B+, A&B, B&C, or C&D? Or should I scrap it and start over, or possibly add a fourth “stage” to it?

    Also, my OT is a Hammond 125E, but I assume if I get the impedance close to 15k for my 8 Ohm speakers, that should be ok, right?


  180. 1st question:
    After reading all the comments above, I purchased a PT 263AX from Hammond for 120V AC use.
    I was wondering if it’s ok to wire my PT to diodes as shown on the schematic in the following URL links, like the 269EX PT.

    If it’s ok, wouldn’t changing the number of diodes from 4 to 2 affect the B+ voltages greatly?
    Also, I have some UF4007s. Can I use them instead of 1N4007?

    2nd question:
    263AX spec reads 5V 2A for the heater taps which are 1.3V different from FcKw’s schematic.
    Will this be a problem(such as heater/filament starvation)?

    3rd question:
    Could anyone tell me the main(best) grounding locations for the circuit? How many locations should there be to minimize hum?

    Thank you guys in advance.

    • Hi,
      263 PT is no good. Should have been 269. The 263 has a 5V filament secondary designed for rectifier tubes, not for ordinary preamp and power tubes. Also, if you wire the HT secondary with only 2 diodes like on the schematic included, you’ll only get 100V on tap. You need to wire the 4-diode bridge and just leave out the center tap.

  181. hello, i will try this project, thanks for post it!
    can someone PLEASE send me the layout (or wiring diagram) and a BOM ?

  182. Would it be possible to modify the preamp stage to emulate a black face fender twin reverb? It’s already quite close so shouldn’t need too many changes.

  183. Lorenzo Says:

    Hi FcKv can you tell me what are the specifics of the fuse and what type of capacitors do you have used ?

  184. Hi, i build your amp, very good sound !!
    I just have one question:
    My ECC99 get very VERY hot !!
    The trim is set at 150R
    How could i check the bias current with my multimter ?
    Just to be shure.

    Thank you.

  185. Hi,
    150R is way too low and that’s why you get the ECC99 very hot.
    Check the voltage at the 150R (between both ECC99 cathods and ground). You should get about 8 or 9V. Ohm’s law dictates that with a 150R, you get around 50-60mA. That’s 25-30 mA per triode and this is in the very upper limit, way too much IMO. Adjust your trimmer to 300R or may be 250R, but not lower.
    However, even with lower figures, you still cannot touch the ECC99 without going ‘ouch’! That’s the way it is. A good tube when run a little hot.

  186. Thank you duke Says,

    I have 6.6v between cathode and ground on the ECC99, with 150R

    And the sound seems good to my ears.

    Do you think it’s ok foe the tube ?

  187. That means a 22mA bias per triode. Now, what is your B+.
    Quelle tension mesures-tu aux anodes de l’ECC99 ?
    Soustrais 6,6V à cette tension et multiplie le tout par 22mA, ça te donnera la puissance dissipée par triode.

  188. J’ai 202 V au B+
    Donc je fais 202 – 6,6 = 195,4 X 0,22 = 42,98
    C’est ça ?
    Ca fait 42% de dissipation, si j’ai bien compris, est ce que c’est correct ?
    Je débute en biasage des tubes 🙂

  189. Une erreur d’un zéro, là tu multiplies des volts avec des mA, il faut donc faire 195,4 x 0,022 et ça te donne la puissance en watts, soit 4,3 watts environ. La fiche technique de l’ECC99 dit que le maxi est 5 watts par triode. Tu es donc théoriquement bon. Un peu élevé si on applique la règle de ne pas dépasser 70 % du maxi. Là, si tu divises 4,3 par 5, tu es à 86 % du maxi. Si le son te convient, laisse comme ça. C’est aussi ce biasage chaud qui donne le son. Moi le mien je l’ai un peu trop bidouillé et je trouve qu’il n’est véritablement bon qu’à fond. Or, ça sort quand même pas loin de 3 watts, ça décolle presque le papier peint. 😉
    file ton mail (codé) si tu veux échanger plus d’infos.

  190. Avec plaisir : tsaddeous at hotmail point fr
    Toutes ces infos sont très précieuses, merci beaucoup !

  191. I’ve built a couple of amps before and this may be a novice question but here it is. I am trying to draw a layout from the original schematic on the mini amp 2.0 and I am just not sure what the A, B, C, and D on the top are. Are they the pots and if so which pin?

  192. Richard W. Smith Says:

    Looking for mini amp 2 Turret board layout. Thank you Rich

  193. chongwen wang Says:

    sry, I have some very weak questions to ask.I have little knowledge of the circuit, so I would like to ask:
    1. what is the connection of these three tubes, and what is the order of their pins?
    2. if I am in a place where it is difficult to buy the ecc99, then I can use other models instead?

    thx very much!!!
    bty,my english is terrible too 😀

    • 1. Please look at the datasheets for those tubes, the pinout is descripted there. You will find these with google.
      2. You can use a 12UA7 or 12BH7 instead, for example. But you have to rebias the ouput stage and you will get a slightly different tonal result and output level.

      • chongwen wang Says:

        thanks !!there are two more questions:
        1、What is the function of P2?
        2、What are the parameters of the four diode in the power supply section?

        Thank you again for your guidance

      • chongwen wang Says:

        oh,sry,there is one more : could u add a fx loop on this amp?

      • Only with adding some additional circuitry that buffers the loop. Additional tubes would be needed or a opamp solution.

  194. Izzy Madhatter Says:

    Hi, after 3 years of having it built and using it, I’m back. I think about the following: Since I use a lot of different sounds I like to use a MIDI guitar Preamp like ADA MP1 and build a 1 Watt 19″ Rack Poweramp using your schematic. To have more flexibility I’d like to add a presence control and a power attenuator. If I crank up my amp it is still pretty loud!
    – I could use your schematic just from the phase splitter, right?
    – TO add presence to the poweramp, I need to install feedback loop from the OT secondary to the phase splitter?

  195. FcKw, I build my own amps and up until now I have stayed away from the “mini amps”, I never heard one I liked until now. This amp is AMAZING! Well done, this tiny little thing has a huge sound and some of the tones just blew me away. Once again, well done.

  196. My miniamp 2.0 build. Toroid transformer is inside the chassis. I added master volume control.

  197. Hi FcKW got a question for you, If I crank the gain all the way and with master volume cranked to the max, I am getting self oscillation from the amp but if I roll back the gain to about 80% it stopped. what do you think might be the possible cause?

    • Hi Tim, check your wiring for audio wires with the same phase getting to close to each other, so that cross talk is happening. Keep in mind that on every triode stage the phase is switched. Also audio wires that are to long could lead to oscilations. If you cannot seperate two wires that are to close, you can also try to use shielded wire.

      • Thanks for the reply! I poked around with my drum stick while the amp is hot. I did something really stupid during wiring I didn’t tie down the output transformer wire so it was hanging above the gain control wire lol. Anyway Oscillation is gone and I re-biased the power tube it sounds even better now.

  198. It’s look and very nice. Just for working at home.
    Can you send me the BOM. Thanks

  199. Ivan P Says:

    Could someone send me the BOM please? Thank you

  200. Hello 🙂 Is there any PCB of this layout available , or even turretboard schem? I’am total noob and I would be grateful for some info.

  201. Francois Poirier Says:

    You should sell it as a diy kit

  202. I’m working on my final build of this amp. I’ve been using it to play live for months now and I love it. One question I have though is this: Does anyone else have trouble with the EQ not being extremely useful? Each of the controls seem to be dependent on one another and the mid and treble seem to do pretty much the same thing. I’ve been over it several times and as far as I can tell, I have it wired correctly. Any suggestions?

  203. Russell072009 Says:

    Hi FcKw. I have been searching for a low power tube amp i can use to create a stereo version that won’t blow me out of a room. Your design looks like a great starting point. I’ve done some work with solid state amps but tubes are new to me. What i can’t figure out is where i would split the preamp to stereo, It looks like between C13 and R21 but i’m not sure what to do with what looks like a feedback loop with R24. I want it to be as clean as it can be and from what i understand the feedback loop helps the preamp from getting too muddy. The end result is going to be a stereo amp with built in reverb and chorus. that’s why i want the stereo option. I know i’ll have to use a much larger power transformer to handle the extra current from having more tubes. i’m also going to have to figure out a reverb circuit but i need to find the preamp output first. Any help would be appreciated.

    • I guess it only makes really sense with stereo input? Then you would have to double everything and link the gain, tone and master controls with dual pots. Just the power supply could be shared. But I have no experiences with stereo designs, perhaps you could have a look at some other stereo designs to get an idea of what are the requirements and changes to be made?

      • Russell072009 Says:

        Ok, let me explain the intent a bit better. i have a crate 120 2×12. it has built in chorus and stereo power amp. in normal mode left and right are fed from the preamp. with chorus on the right channel switches to get it’s signal from the chorus circuit. i have used chorus pedals on mono amps even ones with 2 speakers but having the chorus take over one channel gives it a lot more depth. so really i only need to duplicate the power stage and keep the preamp mono for this to work. i’ve just never seen a tube amp set up this way so i have no real references to use. i can’t tell where the preamp output signal would be tapped. i can send you the schematic for the crate i have or you can look up a crate g120c if you like.

  204. Russell072009 Says:

    Hi FcKw

    This is what i came up with. I have not added a chorus circuit yet. i’m still working on which circuit i want and how to power it.

  205. I have this amp made in 2011 and did not use it for a long time. I start resent using this amp again and the children complain about a high pitched noise. My wife and I can not hear this beep. Probably the amplifier is oscillating (15 k?) How can this be fixed ? No fun for the kids to play guitar.

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