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Scott 299C With Issues

Posted by Jeff Joseph (M) on March 22, 2006 at 17:37:21

I've been working on a Scott 299C. (7591 Outputs, SS Bias Rectifier)

I replaced the first filter cap with a 50/50uf 500 Volt cap (bridged the two sections) and the selenium rectifier with a silicon one.

Brought it up on the variac, put bias at -23 volts, and everthing seems fine until I attempt to bring up to full power (bout 123 volts)
The B+ is little too high, I get 510 volts on the output transformer winding and around 480 volts on the plate.

Something in the amp doesn't like that high a voltage and begins to vibrate (almost a hissing sound from the chassis)(maybe the rectifier?) until I back the variac down.

So - how can I drop the B+ by about 10-15% on this 299C?

Jeff

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