Ampeg B-15 Heritage amp circuit.

[mark]

I recently saw the circuit diagram of this amp and I was a little surprised. It was supposed to be a 64 (B15nc) version and a 68 (B15nf) version in one amp, but it leans more to the 68 B15nf amp.

Immediate differences is the power supply has a choke in the Heritage amp whereas I see a 1K resistor in the 64 and 68 amp. I don’t doubt the Heritage is quieter for using the choke.

If I look at the B15nc and B15nf schematics I can see where George got his ideas from. The trouble is the P.I. stage of the amp is more like the earlier B15na amp and the B15nf, in that it will have greater voltage output with the 120K plate resistors then the 47K plate resistors used in the B15nc amp. I assume these values were used to make up for tone stack losses in the 68 preamp?

The 64 version uses also used 470K plate resistors where the Heritage uses 220K plate resistors. Initially, I might think there was more voltage gain with 470K plate resistors, but the loading of the tone stack probably would make short work of any additional gain.

Time permitting George, could you please explain some of the changes that you implemented in the Heritage B15 amp?

Regards

Mark