Dating fender bandmaster reverb
Bias: Fixed, Adjustment Pot Rectifier: 5U4GB Comments: AA568 included a major change to the bias section of the power amp which was poorly received so Fender changed the model design to the AA1069 but kept much of the disliked circuitry.
The aluminum trim was deleted from cabinets when the AA1069 model appeared in 1970.
Yes of course some have the mid knob and bright switch while others don’t.
All these ab763 amps with reverb has the gain stage in the reverb recovery circuit which the non-reverb amps don’t have.
Take a look at this ’62 Fender Princeton Amp, and you’ll see that exact speaker, as well as the typical Schumacher transformers (EIA 606) used in Fender amplifiers.
Other things to look for include chasses placed in cabinets from a different year, “doctored” tube charts, non-original control plates (usually reproductions) on silverface amps, original transformer bell ends (they have correct date codes, of course) on non-original transformers, and non-original knobs (either repro or silverface knobs on blackface amps).unusual things can be found such as the empty “Pulse Adjust” hole on the rear of early ’60 brown amps, the “middle” volume control, use of tweed style grill cloth, strange non-documented transitional circuits, and changes in tolex color including the super-rare cream colored “brown” tolex that is found on some late ’60 amps. Given that people may refer to this information seeking specific production quantities of amps they are curious about, it should be pointed out that the serial numbers apply to chassis types, and not specifically to amplifier models.
In 1970 a grounded AC plug and three-position ground switch were added to the rear panel.