Tuesday, August 13, 2013

Bassman 10 Normal Channel Conversion

A friend of mine bought a Bassman 10 from me a while ago and he's never been satisfied with the normal channel tone and wasn't into bridging the channels. The tone stack setup is quite different from other Fenders of the era and perhaps Fender was trying to do something with the tone stack that makes the amp more amenable to playing bass through it. Whatever the reason it didn't do much for guitar tone.

It's a sealed enclosure 50w combo based on Super Reverb architecture with a very strange speaker setup. The running impedance is 8 ohms but the amp uses four 32 ohm speakers to get this. The original speakers are as scarce as hen's teeth because of the weird impedance.

A brief  runup revealed that it was exactly as he had said-the bass control on the normal channel did absolutely nothing with a guitar.

After some thought it occurred to me that I could modify it to look like an AB763 normal channel without too much trouble, needing only the addition of five capacitors, two resistors and some nice yellow pushback wire. After comparing the layout to the board I had, I removed the components that needed to be replaced or substituted and wired from the right to the first cathode capacitor and resistor. I then cleared off the wiring for the volume and tone controls and the bright switch and wired them up according to the layout.

Of course it worked like a charm. I'm inclined to do the same thing with my Fender Bantam bass amp when I have a spare hour which according to the pictures I took of it has the same semi goofy tone stack.

The first three pics show the original goofy setup, the fourth shows the completed installation and the last shows what is involved from the AB763 layout diagram-thanks, Fender.

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