Dating fender bassman cabinet
You’ll need schematics to implement some of these mods. We usually start with explaining a mod from a functional perspective where we relate to components in the logical schematics diagram.
The blackface and silverface Bandmasters are medium/big sounding amps with a flexible speaker impedance of 4 ohm, allowing anything between one and four speakers (8 ohm each) to be connected via the main and/or external speaker jack.
Let’s study the blackface Bandmaster AB763 and blackface Bassman AA864.
They are similar in the way that both are clean sounding with just one 12ax7 tube in the preamp stage (vibrato ch in bandmaster and normal channel in bassman).
Speakers The Bandmaster’s 2×12″ speaker cabinet was from the Fender factory loaded with either Jensen C12n or Oxford 12T6.
Personally we favor the Jensen C12n for their natural and transparent “Fendery” tone and, most importantly, for not being to bright and harsh.