– You need to insert a 100 ohm resistor between the left side of 22 k Ohm resistor to ground (the new entry point of the neg feedback loop in previous step).– Between the second preamp tube (V2) and the phase inverter circuitry, replace the 0.1u F coupling cap with a 500 p F.At the Fender factory they used old tube charts when new models came, probably because the tube layout was the same.

rowupdating keys - Dating fender bassman 60

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.

From right to left: – Switch the polarity of the two wires coming from the output transformer going to the speaker terminals.

You need to do this only if you change the negative feedback loop to AA864 specs.

During the different eras the Bassman amp came in many different shapes and configurations.

Few other models experienced so many changes in terms of looks and tone.

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.

All models have a push-pull (class AB) dual 6L6GC power amp configuration.

Up to the blonde Bassman with blonde colored tolex (circuit 6G6) they all had tube rectifier, but since then a diode rectifier was used.

The NBF theory is that you take the signal from the speaker output, let it go through a resistor and mix it in at the entry point of the phase inverter.