Audio Zone amp

Here's a schematic I drew of an  amp made by a local builder. It's pretty much derived from  a Fender Princeton and some of the values here may be not exactly correct especially in the tone stack as I did not have the time to do a full autopsy. It's presented here for reference. The bias network, power section, phase inverter and second gain stage are all accurate to the sample I had with the exception of the raw bias dropping resistor which I believe is 100k. The AC bias voltage from the power transformer is substantial.

This amp was built with a second hand circuit board and the execution left much to be desired. Had it been mine to choose I would have added an additional filter capacitor to the high voltage string down near the first gain stage ala Princeton.

As it was all I was asked to do was to make it work, which took an inordinate amount of effort for such a simple amp. In retrospect it would have been far better and more efficient to make a clean circuit board and just go ahead and replace everything and make a proper job of it.

Making it work proved to be a struggle and after nearly everything had been gone over with a fine tooth comb, the fault turned out to be an intermittent power supply capacitor-a JJ dual can number.

That did it for me. No more JJ capacitors are going in anything I touch.

The Hammond power transformer delivers the goods but the gain on this amp is minimal. It makes a nice 8w amp for very small venues like a practice amp. I am going to try my Boosta grande and see if that gets a little more effort out of it.

Either way, I'm done with it.