I have completed a build on a ’57 Twin combo amp. I really like the 30 -50 watt amps that use a push-pull, 6L6 output configuration. With this build I decided right away that I would use the Sozo premium caps, add an adjustable bias for the power tubes and a slight mod in the input section. The “front end” of the Twin is a bit different from the Bassman.
Each input uses ½ of 12AY7 into another 12AY before the power section. I changed ch 1’s 12AY and put in a 12DW. And put in a nice balanced gain and balanced triodes 12AX7 in the phase inverter circuit. I also used late distortion Svetlana power tubes.
Back to the ch 1 mod. So, the 12DW is an interesting tube in that ½ is a 12AU style and ½ is a 12AX style. I installed a switch so that the player can switch between the two styles of tubes to alter the gain going into the tone section. This can work extremely well with boost and distortion pedals. And left in a jumper to “jump” the ch1 signal to ch 2 and mix in a bit of “bright” sound using the standard 12AY circuit.
A side note about 12_ _ 7 tubes. The AX, AY, AU tubes have different gain structers which an amp designer can use to create how an amp will sound. The AX has a gain factor of 100 while the AU has a factor of 40. What this means is the AU will sound cleaner until it is pushed hard, and then break up. The AX style will distort faster with a different break up tone than the AU. The AY has an even different gain and current factor. Pretty neat stuff.
Anyhow to wind up the build I used Eminence Cannabis Rex speakers to deliver a nice smooth tone across the guitars frequency range. My guitar guru Kris says, this is a great amp for blues style player and sounds incredible with a boost pedal.