– Remove the 220k feedback resistors from each of the plates on the two 6L6 tubes.
You will get more breakup and distortion and more volume at a given volume knob setting.
All models have a push-pull (class AB) dual 6L6GC power amp configuration.
The picture below shows a 1969 transition model amp.
Unfortunately the Bassman was one of the first amps that CBS laid their hands on after buying the company from Leo Fender.
A couple of things in the circuitry were immediately changed in 1965 when the AA165 and AB165 replaced the AA864.
Amp collectors and idealists often prefer the pre-CBS models but if we study the AB165 circuit it does have something very interesting for guitar players who enjoy cranked Fender blackface tones.
We will further focus mostly on the AB165 vs AA864.
Some things have not changed since the beginning; The Bassman never had reverb or tremolo.
At the Fender factory they used old tube charts when new models came, probably because the tube layout was the same.
Determining production date by serial number and transformer codes is better, and you should also inspect the circuit to be completly sure.
The bassman was a combo amp in the tweed era with the 1×15″ and 4×10″ speaker configurations.
From the blonde era Fender made the Bassman as a amp head and 2×12″ closed cabinet. The video below compares a Bassman AB165 to a Princeton Reverb and a Deluxe Reverb.
1) Combining the AB165 and AA864 The schematics for this amp is explained below.