One channel on stereo amp blows filter cap on negative rail

If you don't have a variac, put a 60 watt light bulb in series with the hot side of the AC in. If the light glows brightly, your amps are still drawing too much current or there is a power supply fault. Once you find the problem, the light will hardly glow after the initial currrent rush and the bulb will usually keep the outputs from blowing if there is still a problem. Chuck

if the -22 supply has failed, due to a blown diode or fuse, and if the output transistors have shorted, then the -22 rail will be pulled positive and that will blow the capacitor.

Also note that the schematic has errors on it, for instance the output transistors have emitter and collectors reversed!

Hope you didnt wire the new ones in like the schematic!!

Ancient_Hacker wrote: > if the -22 supply has failed, due to a blown diode or fuse, and if the > output transistors have shorted, then the -22 rail will be pulled > positive and that will blow the capacitor. >

I thought that at first too but if you zoom to 300% you'll see the emitter marks where they belong and the 'squiggles' on the collectors may be a 1970's version of heatsink. You'll see the same marks on the collector of Q312 indicating it is thermally coupled to the heatsink with the outputs.

Way back in the days when I worked on stereo gear I had a unit with very bizarre distortion. It turned out to be a transistor with a 'leak' which on a curve tracer showed up as a transistor in parallel with a resistor from E to C. If Tiger has a similar quirky part it may explain why he's having such a bad time with that amp - which is pretty straightforward and decent for it's day.

G=B2