This amp came about after some discussion at Wattkins.com about the new 1 watt Marshall amps. In the Wattkins Tone Per Buck section much discussion ensued (thanks to everyone who chimed in) and it was agreed that a 1 watt amp could be built at a fraction of the cost that produces as good or better tones.
The first attempts were using a triode, push pull output section and guesses at what sort of topology the Marshall amps were using. I tried a 6SN7 and a ECC99 (actually a 6N6P) in a push pull arrangement, a design basically like my JCM5E3 but with a dual triode for the output. Though the 6N6P was a big improvement over the 6SN7 I still wasn’t sold on triodes for the output tubes..
After getting a little discouraged by the triode output tubes I had been using I decided to look into some low power pentodes. I like cheap Russian tubes and I happened to come across the 6F4P mentioned on AX84 I believe. This tube is the Russian ECL84 equivalent and has a pentode and triode in the same bottle. They were really cheap so I got a few, I think I paid 5 bucks for 6 of them.
To keep the wattage down I went single ended and changed from a Marshall topology to a Trainwreck. With the extra triode in the 6F4P this amp just needed a 6N2P to do 3 gainstages and the power tube. I also think a Trainwreck pre seems to do well in a single ended format.
As soon as I fired it up I knew I was on the right track. The pentode in the 6F4P is very sensitive so I had to add a voltage divider before it. The tone stack is pretty much taked from the Liverpool but I increased the treble cap from 50pF to 100uF to get a little more mids. The tone stack is flexible enough to go from Voxy/Blackface scooped tones to more Marshall like tone by cranking up the mids.
Another, slightly unusual thing, is the negative feedback setup. I tried to “fix” two things with the NFB. The first is a little harshness on the high end. The other is the amount of low end available with a 1 watt amp. So I added a little NFB to fix the sorta harsh high end but added a .0047 capacitor so the NFB would not affect the low end. This gives a perceived low boost while smoothing the highs. I really like how it turned out.
For iron I’m using a Weber WSE15 for the OT. It’s way overkill but it’s the only single ended OT I had. The PT is an Edcor XPWR024-120.
At this point I still haven’t heard any of the 1 watt Marshalls other than YouTube clips. I can say I’m really happy how this one came out. It could also be built for about one tenth the cost of the Marshalls. A 1 watt Trainwreck style amp is fun to play and not worry about disturbing everyone in the neighborhood.
Here is the schematic.
And here is my layout.
Here are a couple clips:
The speaker in this one is a 2×12 with a Celestion 70th Anniversary and WGS Veteran 30. Tone controls are at noon and volume is around 2 o’clock.
The speaker here is a Jensen MOD 12-35 in a small 1×12 cabinet. Tone controls are at noon and volume is around 2 o’clock.
Here’s one more clip.
Very nice amp projects!
Hey there, I’m going to make a TMC1 soon, i have the tubs and am sourcing the transformers. It looks like the Weber OT you used is 5K to 8ohm, is that ok for the 6F4P? 5K OT seem to be more available and cheaper than 10K transformers are. I’m asking EDCOR if they will make a XSE10-5K with 8 ohm rather than 6 ohm tap.
Nevermind! Just found the wattkins thread where you discussed this. Looking forward to making this. cheers