Start Dating fender bassman amp

Dating fender bassman amp

The picture below shows a 1969 transition model amp.

– Replace the 0.022u F coupling caps in front of the 6L6 to 0.1u F.

– Modify the negative feedback loop from the AB165-design to the AA864/standad Fender NBF design.

The .1u F cap you are about to remove may be used later as coupling cap between phase inverter and power tubes.

The negative feedback loop ends up at the left side of the 22 k Ohm resistor which is a new soldering point.

1) Combining the AB165 and AA864 The schematics for this amp is explained below.

The red circles in the schematic below illustrates these changes.

We’ll come back to this later in the “blackface chapter” below where we’ll demystify some of the hypes with the popular AA864.

The AA165 is very rare and its circuit and tone is quite similar to the AA864.

A couple of things in the circuitry were immediately changed in 1965 when the AA165 and AB165 replaced the AA864.

Amp collectors and idealists often prefer the pre-CBS models but if we study the AB165 circuit it does have something very interesting for guitar players who enjoy cranked Fender blackface tones.

(click on image to view full size) 2) Negative feedback loop The negative feedback loop can easily be tweaked to alter the treble cut and distortion in your amp.