Dating fender amps tube chart
The main differences between these amps are transformer size, filter caps size and output/speaker impedance.
Yes of course some have the mid knob and bright switch while others don’t.
Many silverface and some blackface amps have the exact week, month and year stamped insie the chassis.
Summary The Bandmaster came with many different circuits during the blackface and silverface eras.
Hence, the AA864 Bassman normal channel has more preamp “juice” and reaches the sweet spot at an earlier volume knob setting.
The Bassman has a slightly bigger output transformer resulting in a firmer tone and more attack.
The blackface Bandmaster is therefore ideal for those who look for a pure Fender clean sound without making ones ears bleed.
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).
The vibrato channel in the Bandmaster is even more clean than the Bassman because of the vibrato circuitry loading the signal chain and reducing the gain level in the premp section.
The first of the three digits tells us the last digit of the year (unfortunately not decade specific) and the last two numbers tell us the week.
In the above example, the transformer was made in either 1966 or 1976, week 45.