Dating fender guitar
Remove the 0.1u F cap and 47KOhm resistor in the feedback loop and replace with a 820 ohm resistor (which you can make switchable by using the ground switch).Personally we have experienced good results with a 1.5K which reduces the negative feedback and increases distortion and treble.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.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.Production years 1964 -1967 “blackface” circuits AA864, AA165, AB165 1967 -1977 “silverface” circuits AA165, AB165, AA270, AA371, AA568, AC568, AA864 Tube layout AA864 Tube layout (Seen from behind, V1 is to the right side): V1 12ax7 = Preamp bass channel V2 12ax7 = 2’nd gain stage bass channel (and normal channel for AB165) V3 12ax7 = Preamp normal channel V4 12at7 = Phase inverter V5 6L6 = Power tube #1 V6 6L6 = Power tube #2 Summary The Fender Bassman is a legendary guitar amp known to both guitar and bass players.
The AA165 is very rare and its circuit and tone is quite similar to the AA864.The next time you get into a Fender Bassman discussion you should narrow down exact which era, model and circuit you’re discussing. The tube charts are not very useful for determining the circuit model.A lof of blackface Bassman amps with AA864 tube charts are actually AA165’s, and a lot of AA165 charts are glued into AB165 amps.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.
All models have a push-pull (class AB) dual 6L6GC power amp configuration.