Microphonics When Hot, Raytheon CK5842

CLS · 5th September 2005, 05:08 AM

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.

PRR · 5th September 2005, 05:14 AM

> [i]Is this normal on such tubes?

Yes.

> Is it because the ....ventilation is insufficient?

No.

CLS · 5th September 2005, 05:23 AM

PRR,

Thanks a lot for your quick answer.

I'm always thinking you are one of the coolest guy in this forum

5th September 2005, 05:08 AM	#1
CLS diyAudio Member Join Date: Jun 2005 Location: Taiwan	Microphonics When Hot, Raytheon CK5842 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.

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5th September 2005, 05:14 AM	#2
PRR diyAudio Member Join Date: Jun 2003 Location: USA	> [i]Is this normal on such tubes? Yes. > Is it because the ....ventilation is insufficient? No.

5th September 2005, 05:23 AM	#3
CLS diyAudio Member Join Date: Jun 2005 Location: Taiwan	PRR, Thanks a lot for your quick answer. I'm always thinking you are one of the coolest guy in this forum

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