Fuzz and crackle sound on right channel [resolved]

Bottle Rocket · 2170

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Offline Bottle Rocket

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on: February 17, 2016, 03:31:43 PM
The right channel has a crackly/fuzzy sound for about the first 10-15 seconds when I turn on the amp.  After that the channel suddenly clears and sounds fine. (However the right channel still has a little more hum than the left).  Just wondering what might be causing this?

- I have swapped the tubes between the amps and this hasn't changed anything.

- I've also turned the amp on then off (disengaging the soft start).  I soon after turn it back on and the fuzzy sound for the first 10 seconds is still there.

Thanks for any insights.
« Last Edit: March 10, 2016, 08:52:28 AM by Caucasian Blackplate »



Offline Paul Joppa

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Reply #1 on: February 18, 2016, 08:35:03 AM
That's about the time it takes for the driver/regulator tube heater to warm up. Could be a marginal solder joint in the Zener string, for instance. That string is inactivated when the regulator triode starts functioning.

Another theory is a marginal connection that stabilizes with the expansion from heating. I feel that's less likely because most items take more than 30 seconds to achieve operating temperature.

How long has the amp been functioning before this occurred?

Paul Joppa


Offline Bottle Rocket

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Reply #2 on: February 18, 2016, 09:21:20 AM
It was functioning for about 1 month (maybe a little less) before this started occurring. 



Offline Paul Birkeland

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Reply #3 on: February 20, 2016, 06:13:55 AM
There isn't really any correlation to flaky joints and when they may or may not appear.  I have worked on ST-70's that had flaky solder joints that didn't produce any problems until decades after initial construction.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Bottle Rocket

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Reply #4 on: February 20, 2016, 11:22:00 AM
Paul, I resoldered the zener string and things have cleared up.  Looks like your first hunch was correct.

Thanks for the help,

Michael