Fuzz and crackle sound on right channel [resolved]

[Bottle Rocket]

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.

 

[Paul Joppa]

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?

 

[Bottle Rocket]

It was functioning for about 1 month (maybe a little less) before this started occurring. 

 

[Paul Birkeland]

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.

 

[Bottle Rocket]

Paul, I resoldered the zener string and things have cleared up.  Looks like your first hunch was correct.

Thanks for the help,

Michael