2W Trainwreck Express


Idea to build this amp came after watching an amazing YouTube video of Glen Kuykendall with his Trainwreck. I don’t need the power of original Express, so I went with a 2W version as posted on AX84.com.


I already had some NOS Raytheon 12SN7GTA tubes, so it made sense to use them and use 12.6V heater voltage for all tubes. Preamp tubes are JJ ECC83s and for phase inverter I got an Electro Harmonix 12AY7. Filter caps are all JJ (one axial and two cans), cathode bypass caps are Sprague Atoms and coupling caps are ERO/Roederstein MKT1813 tubular film caps. Caps in the pf range are silver mica and 1nF ceramic cap is MuRata. Signal resistors are all metal film, mix of nice brown Dale, few Xicon and Beyschlag. Power supply resistors are metal oxide. All plate resistors are rated 2W for lower noise. Output transformer is a 5WPP model from Musical Power Supplies. It’s supposed to have better bass response for hi-impedance tubes than Hammonds due to higher inductance. Power transformer is custom wound (as usual) by Trafomatic. It has a 250-0-250@70mA HV secondary and 12.6V@1.3A heater secondary and is wound on beefier 80VA core. All rectifier diodes are hefty ultra fast UF5408.

Surprisingly, there aren’t any significant mods on this one:

  • 12SN7GTA output tube, should perform the same sonically;
  • 12.6V heater operation. Preamp tubes heaters are wired to pins 4 and 5 with pin 9 left unconnected. Heater elevation voltage is applied to pin 9 of the PI tube;
  • two 2x32uF can caps instead of a 47x20x20x20uF can cap (didn’t have those on stock when I ordered parts);
  • Ferrite bead on the input lead, should filter out RF;
  • 33uF 160V Panasonic radial caps for heater elevation and bias supply instead of 10uF, shouldn’t change anything.
  • 25uF cathode bypass caps instead of 22uF. For electrolytic caps those are within tolerance range.

I like the chassis used on my Black Box Pre. Although it’s not particularly good looking, it’s very nice to work with and allows for each panel to be removed separately. I got the same box, just a bit taller for this project. Tubes, transformers and circuit board are mounted on a metal panel that’s attached to the chassis from inside. That way, you can only see jacks and knobs from the outside, top panel needs to be removed to access tubes and trannies and bottom panel covers the circuit board. That makes a compact build that’s easy to carry around which is important to me. Layout is pretty much the same as in the project file with a couple of changes that made sense to me since this chassis is smaller. Output jack and impedance switch are moved to the front of the chassis, fused IEC socket, power switch and indicator light are on the back to keep AC as far as possible from signal leads. Those ERO coupling caps have a line that (hopefully) marks the outer foil end. I connected it to the lower impedance (input) side to help with noise.

Heaters are twisted tightly together using a hand drill. It’s a great way to twist wires nice and uniformly. Just take two straight pieces of wire, twist them a couple of times and mount the twisted end into a drill head. Have someone hold the ends of the wires and use the slowest speed on the drill. Also, having 12.6V heaters means that current draw is halved compared to the original, so radiation from heater leads should be further reduced.

Preamp tubes’ middle pins are tied together and grounded to the closest chassis bolt. Since the middle pin goes all the way through the socket, having it grounded may help with shielding between two triodes.

Can capacitors are mounted using horizontal claws. This is a great way to spare the builder from drilling enormous holes needed for vertical mounting, when space permits.

Most of the leads that go to the circuit board are threaded through the closest unused hole as shown on the photos below. That helps with strain relief and improves reliability.

Shielded teflon wire is used for input jack to V1 grid and from volume control to V2 grid. It seems to help with noise level.


Click on an image to see more details.


It worked almost from the first try. The output transformer secondary on PP5W has the opposite orientation that expected, so NFB was actually a positive feedback. That made amp squeal like hell. I had to rewire NFB to go to the output jack sleeve instead of the 8ohm tap. That also means that amount of NFB would change when impedance is not set to 8ohm, but that doesn’t concern me since I only use it with 8ohm output.

I wanted to wait until I get used to the way this amp sounds before posting any conclusions. My usual reaction to a new amp or pedal is to not like it. It takes some time to dial in sound that I like and to get used to what it can offer. I’ll go over few different aspects that define how an amp sounds:

  • Gain: it’s got more than expected. It gets dirty with volume control set pretty much anywhere, especially with humbuckers. I found that with amp volume control set at 30-40% it can nail some nice classic tones – Led Zeppelin with humbucker equipped guitars and SRV/Hendrix tones with single coils.
  • Sustain: lots of it, especially with higher volume settings. After maybe 50% on volume control it only ads more compression and sustain. It’s nice for fluid sustaining solos, but to compressed for rhythm.
  • Touch responsiveness: it can do clean-to-mean thing pretty well by using guitar volume control, especially combined with humbucker/split/parallel modes. With high output pickups and guitar volume maxed, amp volume control doesn’t do much as far as clean-to-mean goes, just adds crunch and sustain. In that situation I found that guitar’s volume control and pickup selector switch are more important, combined with pick attack.
  • Tone: it is bright, but not as much as expected from reading on the web. It has to be bright to a certain degree to be able to sound good with lower input volume, otherwise it would be dull for clean and not sparkley. It actually bass that needs to be tamed. I keep bass control at 0-20% all the time. With higher settings it sounds flubby and muddy when overdriven.
  • Noise: surprisingly, it’s got very decent noise level. No oscillations at any volume levels. Trainwrecks are notorious for being noisy and prone to oscillations, but I’m very happy with this build in that compartment.
Update (May 2010)

I’d like to add some bright switch observations. It obviously works well with some guitars and doesn’t with others, but it kept me from getting better tone from this amp for weeks. When you tune into decent settings with the bright switch on, turning it off makes the sound dull and takes some gain away. I would immediately turn it back on, but don’t give up and turn it back on before playing with other controls. To tame the harshness I was backing down on treble, gain and presence but foolishly kept the bright switch on (100pF position) all the time. That would make the sound a bit dull and still harsh. With my Ibanez the opposite seems to be working better – adding a bit of treble, gain and presence but turning the switch off. That makes the amp sound sharp but less harsh than with the bright switch.

Update (June 2010)

I had to add this update after trying the amp with my Strat because it’s a completely different beast! My impressions about this amp were that it had way too much gain when played with my Ibanez. It’s much more tame with the Strat. Transition from clean to mean is slower and has more sweet crunchy tones in between. This is another proof for how sensitive this amp is. Now I’d like to try it with Les Paul 🙂

Useful links

AX84 4-4-0 project page
AmpGarage Forum – great Trainwreck info

21 Responses to “2W Trainwreck Express”
  1. Davide says:

    Very clean wiring, good ideas and detailed information. Inspiring me with my guitar tube amp building project. Thanks a lot

  2. muhammad says:


    I have few questions about the studio 4 4 0 build.

    – the S1 SW DPDT (power sw) that i ordered has 6 lugs. the layout diagram shows 4 wires to be soldered into it. can i leave out any two adjacent lug and wire the rest 4 lugs on the switch?

    link for the S1 : https://www.amplifiedparts.com/products/switch-carling-toggle-dpdt-solder-lugs-0

    – R6, R8 180K/1W required. can’t find these. can i connect multiple resistors in series/parallel to achieve 180K. if so what would be a good option. please explain in details.

    – C16 capacitor; i don’t see it in the layout diagram. is it not used!

    Thank you in advance.

    • bancika says:

      – yes for the DPDT, but don’t leave out the middle two lugs because they are common. If you want to turn the amp on by flicking the switch up, then solder to the bottom two lugs, otherwise use the top two lugs
      – 220K resistors should work fine instead of 180K for those two cases. If you want to get closer, you can use two 100K (0.5w or 1w) resistors in series or if you want to get exactly 180K you can use 220K and 1M 1W resistors in parallel. Either of those options will work ok for this particular case.
      – seems to be a typo on the official layout, there are two C18 caps. One on the board and one on the pot directly. The one on the pot is C16. You can see on one of my pics how I wired those two capacitors on the bright switch http://diy-fever.com/wordpress/wp-content/gallery/4-4-0/bright_switch.jpg

  3. mike says:

    I love the tone of this amp! However, it appears the AX84 site is down. I would like to build this and I can’t find the kit anywhere. I did find a schematic on one site but was hoping for a little more. Any advice?

    • Bancika says:

      I see that chappelamps.com is also down. He was selling kits. You probably have to buy everything yourself, it’s not that hard 🙂

  4. Doc says:

    I’m curious as to what the cost of this project was, not including the head cabinet.

    • Bancika says:

      It’s hard to tell because I bought parts from many different sources at different points in time. I’d say about 200-300$ is right.

  5. Jaume says:

    Hi, Bancika,
    I’m planning to build this amp, probably using a pre-punched chassis from ampmaker.
    That means I’ll have the valves in reverse order, V5 to V2 beginning from left to right, in opposition to the original layout from AX84. I think it’s also what you did, according to the photos. Also, the pots, input and switches.
    Did you change the layout/schematic? I mean, probably it will be better to swap the preamp stage 1 to the pins 1,2,3 from V5, and the pream stage 2 to the pins 6,7,8 to keep their lugs closer to the board. but I’m in pain to make me a mess..
    I think that I have to make like a “miror” with the original layout, is that what you did?

    Regards and great blog!

  6. Anthony says:

    Very nice build. Your title says Trainwreck Express. On the AX84 website I only saw the Trainwreck Studio. Is youre express the same as the 4-4-0 Studio? Just check because Im looking at building this amp soon. Thanks for posting this and I love your website – very interesting.


    • Bancika says:

      It’s ax84 4-4-0 studio (studio meaning 2W output stage)…the circuit is from trainwreck express with modified output stage.

      • Anthony says:

        Thanks for the reply. Ive got those schematics now off the AX84 site. I have a couple questions if you dont mind

        – Could a gain pot be added? Or is the gain easily and usably controlled through the guitar volume as you noted in your description? I may want to play louder with clean – can I do that without a gain adjustment?

        – I would like to add reverb to this amp, but Im unsure about how or where to add it. It would be nice if I could use one of the Belton digital reverb modules.

        – What size enclosure did you use? Im guessing a 17″x8″x2″ or so?? Also, my first amp I built was the P1 kit from AX84. Where can I get a board for mounting components on and install the ferruls? Im in the USA.

        Sorry for all the questions. I appreciate all your help and for sharing the info on your site with us all.


        • Bancika says:

          volume control IS the gain control 🙂

          belton reverb is not really suitable for this amp because it requires low level signal and you will not find it here 🙂 You need an amp with FX loop that brings down level to line level that may be used with digital reverb.

          Don’t remember the size, but it was around14x8x7

          Try http://turretboards.com


          • Anthony says:

            Thanks for the website – its very useful for sure. I was thinking of an additonal circuit much like a FX loop being added to this amp with a recovery stage. Maybe its much easier to just use a reverb or delay pedal with this amp. How does the amp take pedals?

            Would you say this is the overall best low watt amp you have built? Im looking for someing in the 3-4 watt maximum range for playing at home. Is there a different amp that you might suggest?

            Thanks for the help.

  7. smacko jack says:

    senor bane; I have been reading your site much of the day today. I just found it so had some real catching up to do. It’s a great site BTW, thanks. I notice you like to run the heaters in series with 12.6 volts. I am new to building amps but have done several. I have not done any with series heaters at 12 volts though. Do you recommend that setup for other people to try?

    thx, jack d
    Nebraska, USA

    • Bancika says:

      In that particular case 12SN7 required me to use 12.6V. Using 12.6V instead of 6.3V has upsides and downside. When you double the voltage, the current will halve, so EM radiation around heater wires will halve and thus risk of heater noise will reduce. On the other side, 12.6V doesn’t let you use russian tubes 6N2P and such…

  8. TAJ says:

    Hey, I love it.

    The 2W trainwreck sounds great, but a bit thin. Can it be thickened up with a better output transformer, or bigger coupling caps, or something? Maybe it’s just the pickups you’re playing with. Single coil?

    What are you using for output? Is this just small-signal straight to recording, or are you playing through a speaker and mic’ing it? Just curious.

    • Bancika says:

      Hi, thanks for the comment!

      You know, I’m not 100% happy with is either, but I can’t tell why. It’s not pickups for sure, most of those clips are recorded with Petrucci signature DiMarzio’s. You can hear them through my other preamp here http://www.youtube.com/watch?v=VELiL7SExGE&feature=related
      I don’t think there’ anything wrong with the OT. It’s higher inductance than any hammond tranny, it’s built for high impedance load.
      Amp is run into the dummy load and then tapped through palmer PDI speaker simulator (the same simulator is used on that clip I mentioned). Maybe that’s the reason I didn’t like it too much. For apartment it’s too loud through speaker (yeah I know it’s only 2w). Dummy load makes it sound…I dunno…dull 🙂


  9. Jim says:

    Bane – Nice build – as always, great work and great chops! I like the new look of the site too!

    I’ve started building my 5E3, finally! Need to do some fabrication (metal work) on the chassis – this is the part I hate.

    Take Care and see you on the forums –


  10. mEaT_hEaD says:

    u hav teh mad buillder skillz!

  11. Matt says:

    Nice looking build! It’s great to see that OT5PP move from my garage workbench to a neat project in Europe! I’ve been getting a lot of project activity on this and am going to run a lot offshore & should be able to knock a few dollars off it soon.

    I like the way you’ve got your web pages are organized. Lot’s of good ideas and info here!

Leave A Comment

  • About

    The idea behind this site is to share my experience with Do It Yourself approach to guitars, amplifiers and pedals. Whether you want to save a couple of bucks by performing a mod or upgrade yourself instead of paying a tech, or want to build your own piece of gear from scratch, I'm sure you will find something interesting here. Also, this is the home of DIY Layout Creator, a free piece of software for drawing circuit layouts and schematics, written with DIY enthusiasts in mind.