This amp is an attempt to get some nice cranked up Marshall tones out of a little single ended amp with just two tubes. It’s packing one 6N2P (Russian 12AX7) and a 6V6. It’s built in a little fuse box so I don’t have any room for more tubes.
I originally wanted a tone stack but after some experimenting found that, with only 2 tubes, the tone stack took too much gain away. I still worked in a bass and treble control but they are individual controls. The work pretty well and don’t suck a lot of gain. Just what I wanted.
The circuit is similar to a Fender Champ but the first triode is set up to boost the highs and mids. To me, this is one of the main ways to get that Marshall type sound. Without a tone stack there is no real mid scoop but I think it still works well.
The basic deal is 2 gain stages and the output tube. The cathode on the first triode has a cap on a pot which acts as the bass control. With the bass all the way down the first triode just has a .68uF cap on the cathode. By turning the bass control a bigger 22uF cap is brought in to increase the bass. The treble control is a simple high roll off after the volume pot.
The transformers are ones I had lying around. I had them so I had to do something with them…A Weber RVBPT for the power transformer and the output transformer from my Valve Junior. The plate voltage is fairly low at 333vdc but I’m going for a dirty amp here so I think it works OK.
I think it does capture a lot of the Marshall type vibe for an amp with just two tubes.
Here is the schematic: