Mystery intermittant preamp noise

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rotarius

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Mystery intermittant preamp noise
« on: 23 Dec 2020, 05:39 pm »
I have an old Audio Electronic Supply AE-3 that has developed this issue that I am pretty sure did not exist before.  Without an audio signal and regardless of volume position there is this static "putt putt" noise that occurs every 2-3 minutes and always in pairs only.  It is not the tubes or the environment because it occured in my previous home as well regardless of tubes used. I never hear anything strange during music playback but as soon as music stops, there it is.  The .22uf coupling caps and the output caps were replaced a year ago.  Sounds glorious with the Audiocap Theta and Claritycap ESA combo.
Looking for ideas on what to check next. Thank you!

FullRangeMan

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Re: Mystery intermittant preamp noise
« Reply #1 on: 23 Dec 2020, 06:48 pm »
Seems it will demand a tech inspect under the wood, as AES was owned by Cary maybe they could help or email the pdf schematic to you. Do you think it have to do with parts temperature?
« Last Edit: 23 Dec 2020, 08:05 pm by FullRangeMan »

JakeJ

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Re: Mystery intermittant preamp noise
« Reply #2 on: 24 Dec 2020, 02:14 am »
Pictures of the guts would help.  Might be the power supply caps.

AVnerdguy

Re: Mystery intermittant preamp noise
« Reply #3 on: 24 Dec 2020, 03:48 pm »
Back in the old days when dinosaurs roamed the earth and all we had were tubes, we called that "motor boating". If it's in both channels then it's obviously common (B+ rails) and more than likely the power supply capacitors. On a rare occasion I saw the same symptom from a rectifier tube on the way out.

JakeJ

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Re: Mystery intermittant preamp noise
« Reply #4 on: 24 Dec 2020, 05:14 pm »
Ding, Ding, Ding!  We have a winner!

rotarius

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Re: Mystery intermittant preamp noise
« Reply #5 on: 24 Dec 2020, 05:31 pm »
It is in the right channel only.  It is different from a tube motorboating, I have experienced that before.  I could bypass each of the PS caps to troubleshoot but since it is always in one channel, maybe it's the 1.5uf claritycap on that output. What about a bad volume pot? 


rotarius

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Re: Mystery intermittant preamp noise
« Reply #6 on: 24 Dec 2020, 05:33 pm »
And thanks for all the replies everyone!