Tube DIY Asylum

Posted by Caucasian Blackplate (P) on September 17, 2017 at 11:31:47

In Reply to: RE: good push pull 2A3 design schematic posted by vinnie2 on September 17, 2017 at 07:33:22

I would look at starting with something like the Mullard 20W amp as a starting point.

You'll need to lower the B+ a little bit for the 2A3, and I'd assume that you'll run cathode bias instead of fixed bias.

Substitute a 12AU7 or 6CG7 for the 12AX7 (you don't need the gain), adjust the biasing in that stage to account for the tube change. With lower available B+, the AU7/CG7 will be plenty happy with a lower impedance pair of plate resistors.

Lastly, remove the compensation on the driver plate load and disconnect the feedback.

Gain is likely a little higher still than you'd want, and perhaps using half of another 6CG7 instead of the EF86 will give you a driver stage that isn't overly sensitive.