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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 6th Jul 2022, 6:21 am   #41
Diabolical Artificer
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Default Re: Heathkit S-99 distortion after operation

If it's self oscillating you should see it on any scope and or be able to measure it with a half decent DMM just use a dummy load with no input and slowly turn the volume up.

Andy.
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Old 7th Jul 2022, 11:18 am   #42
qualityten
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Default Re: Heathkit S-99 distortion after operation

Thanks for further advice. With the replacement 47pF capacitors and the replacement of the faulty balance control, it seems to be okay. No distortion now on the square waves through the audio frequencies. The latter test showed me that the treble pot is also mistracking just around the optimal setting, so I’ll replace it too.

Moral of the story: when restoring old, moisture-damaged amps don’t trust the old pots any more than the old resistors!

As always, thanks for all the help.
David
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