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Ampeg VT-22 (distortion model)

December 26, 2018

 

This one came to me with some major problems, allegedly having started on fire(!) at some point. I've seen quite a few of Ampeg amps from this era (the V2/V4/VT-40/VT-22) and while I think they're great, they apparently see a lot of neglect and need some help getting healthy.

 

I love them because they all have original schematics glued to the inside chassis, and the case is designed in a way that makes it easy to access both sides of the circuits boards without having to move or disconnect them. I've also found that other techs are in the bad habit of recapping them by leaving the original can capacitors in place, and just plopping new filter capacitors into an empty corner using rubber bands and hot glue, which I find kind of objectionable.

 

This was a later version of the VT-22 that came out sometime in the mid/late-seventies featuring a slightly different preamp section (a distortion circuit was added, and they did away with the 6K11 triple triode tube that got used in the earlier models.) This one had a bunch of burned resistors in the preamp section. After some hunting I found that a protection diode in the power supply (D206 in the schematic, near the standby switch) was dead, and was causing all the cathode resistors in the preamp section to see 500V on power up, so they all immediately fried.

 

After replacing that one diode (I use BY255 diodes for the power supplies in these amps, rated at 3A/1300V) the amp was finally alive but still needed a lot of attention; the hum balance pot was damaged (a web store called Angela Instruments sells a couple good replacement options for this pot, in this case it was a 100 ohm, 3 watt linear locking pot with screwdriver adjustment), the speakers both had a bad case of coil rub and got replaced, the output tubes and several of the preamp tubes needed to be replaced.

 

 

 

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