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Microphonics When Hot, Raytheon CK5842

CLS

Member
2005-06-17 6:58 am
Taiwan
Hello there,

I built a pre amp based on 5842 (as posted here ).

Using it for a while, I found, after running for 3~4 hours, one of the channel clanking loudly as the stepped attenuator hit the 'off' position.

Then I tried tapping on & unscrewing the chassis, that particular channel would make some sounds on the speaker. (not to mention tapping on the tubes, it's so loud when that problematic tube was hit)

Yes, microphonics!! A big bad one.

I swapped the tubes among channels & the symptom followed that particular tube. I changed that tube & kept trying. By now, I found 2 out of 8 tubes have such problem.

Is this normal on such tubes?
Or they are defected ones?
Is it because the tubes are covered by a conventional box instead of protruding out of the top plate like a "real" tube amp, so the ventilation is insufficient?

Back then when I was building this pre, I'd thought about making the tube sockets "suspended". Somehow I dropped that idea. I should have.