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Re: feedback and/or oscillating tube preamp

216.39.159.41

Posted by Paul Joppa on August 14, 1999 at 13:46:37

In Reply to: feedback and/or oscillating tube preamp posted by e-mail on August 14, 1999 at 04:29:51:

We need more data. Can you identify the issue of Glass Audio, or otherwise provide or describe the circuit? And describe the sound? A continuous whistle indicates an audio frequency oscillation, but a "chirp" can indicate an RF oscillation which quenches itself at a more audible rate. The former would require a larger reactance in the wrong place to get the phase shift right.

FWIW, I had a problem like that with my SEX amp in one of its incarnations - I knew it was RF because the LEDs on my soldering iron would flicker in time with the chirping. I cured it with grid stoppers, a few hundred ohms of (preferably carbon composition) resistor in series with each grid. If you try that, put them as close as possible to the grid pin.

hth, otherwise give us more info and more people can try to help...

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