What to do to the AB165 to make it sound better. 

Pre amp - Take out the 500pf and .01 caps across the 100k plate load resistors. That will open up the
high end. There's nothing else to do until you get to the phase inverter! 

Power amp - Change the coupling cap to the phase inverter to a .001. Make the feedback loop look like
the AA864 by using an 820 ohm resistor and connecting it to the high side of a 100 ohm resistor like a
standard blackface amp has. Change the .022 caps to .1. I actually use .047's here because I think it
tightens up the bass a little bit. Don't forget to reverse the speaker side of the output transformer by
connecting the green to positive and the black to ground. 

Bias suply - Make it look like any other blackface amp. I normally use a 50uf-50v filter cap, but anything
higher than that up to about 100uf is fine. Use 220k grid resistors instead of the 100k's that may have
come later on some AB165's.. 

Power supply - Change all the electrolytics with original values. The extra 16uf in the power supply of
the AB165 (but labeled as an 8uf on the schematic) is a welcome addition and should stay. It would be a
good idea to change the carbon comp resistors under the cap pan with some metal oxide or metal film
ones to reduce noise and popping (or the chance of having it happen later on). 

Some notes: This mod takes a bit of creative thinking to get the layout to work. Fender had a nutty
looking layout with the AB165. Some of the eyelets that you think you want to use could be grounded
from underneath by a hidden wire. Look at the schematcs and layouts so you can figure out what you are
going to do. I'd draw it out, but I don't remember exactly how I do it. It only takes a minute or two of
thinking to figure it out, but you do have to look at it a bit. 


That's it. Now you have an AA864/AB165 hybrid that sounds better than either. The amp compresses
and distorts great, but you still get a good clean tone. Please resist the temptation to be a jerk and do
this to an AA864 model amp. Those amps are rare, and I think most of them were built in late '64
which makes them Leo era amps. Don't mess with them! You can usually find any blackface (AB165) or
silverface Bassman head for fairly cheap to do this to. AA864 heads are off limits for modding as far
as I'm concerned.