Tube Amp Archive

Thanks for all the responses. It was the transformer primary windings. I swapped them and everything's cool. What causes that?

Just finished a CtG FCBN 51B clone of an Ampeg B15N, schematic attached. I have 2.5 kHz oscillation when I power up. I substituted a Hammond 1750Q output transformer because the Weber WOT45HHR-UL they called for was out of stock. Also added a speaker selector switch since the Hammond has 4, 8 and 16...

roberto, I don't think you're supposed to change modes with the amp powered up, at least I wouldn't recommend it.

Structo, that's the highest resolution on their website. If you save it as a pdf and then open it in a viewer you can zoom in. After a little more research I have seen other schematics with a similar setup I'm just not used to seeing electrolytic caps used reverse polarity. I thought they'd blow. I ...

In looking at the schematic of this amp, I noticed that capacitors C13 and C23 in the cathode bias circuit are backwards with the positive side connected to ground. Is this right? The original Ampeg B-15NB schematics show a 50uF inserted correctly. The schematic is here: http://ctgelectronics.weebly...