Amp Tech

Guitar Amplifiers Mods, Amp Maintenance, Tube Amp Schematics, Wiring Diagrams and more.

Fender Tone Stack From Board to Pots Mod

Fender Tone Stack moved from board to pot to reduce hiss, hum and Parasitic Oscillation.

The following tone stack mod will help reduce or remove hiss, hum and Parasitic Oscillation in your Fender tube amp. We will be moving the tone stack of a Fender Blackface or Silverface Amp from the board to the pots. This mod reduces about 2-3 feet of grid wire. Included is a detailed layout of how it's done.

Fender Bassman Amp Tone Stack Mods

Fender Bassman Tone Stack Mods

In this file we will be modifying a Fender Bassman amp tone stack to sound more like the original 59' Bassman or Marshall Plexi on the bass channel and warm up the normal channel a bit. These mods also apply to similar Bassman circuits like the (AA371, AA165, AA864, AC568 etc... ) The Fender Bassman amp tone stack caps include 3 caps in the normal channel (250pf ceramic treble tone cap, .047uf mid tone cap and a .1 uf bass tone cap) and 3 in the bass channel (350pf ceramic treble tone cap, .1uf mid tone cap and a .1uf bass tone cap). Note other circuits may differ slightly in the cap values but the mods are the same.

Fender AB165 Driver Circuit Mod

Fender AB165 Driver Mod Layout

The Fender AB165 Bassman is a great guitar and bass amp, but for guitar it sounds a bit dark, muddy and lacks the high end chime that prior Bassman models where famous for. The driver circuit mod converts the AB165 circuit to sound very similar to older tweed Bassmans like the famous 59' model. After the mod you will have a great sounding guitar amp that takes pedals very well. Great amp for Blues, Blues Rock, Classic Rock, Country, Funk etc. The mods are simple and if you don't like them it's easy to convert back to the original circuit.

Fender Blackface Bassman AA864 Wiring Diagram and Schematic

Fender Black Face Bassman Amp and the Bassman 50 Silverface

In 1964 Fender introduced the "Blackface" design, with black tolex covering and a black painted control panel. Fender was sold to CBS in 1965, but this design continued until the "Silverface" model was introduced in 1968. The Brownface, Blackface, and Silverface "piggyback head" (except the Bassman 10 and 20, which were also combo amplifiers) versions of the 1960s, 1970s, and early 1980s generally followed a trend toward cleaner sound and more headroom.

Fender Mid Range Control Pot Mod

Add a Mid-Range Pot To Your Fender Amp

This file will show you how to add a mid range pot to your fender amp. Instead of adding a mid pot Fender often used a fixed 6.8 resistor instead. The 6.8k resistor is soldered to the bass pot (2 lug) wiper to (1 lug) ground with the (3 lug) left untouched. You can also replace the 6.8k resistor with a 10k resistor for more mids without a pot or a lower value for less mids.

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