Traynor YGL-3 noise when coming off Standby

[mhuss]

This amp made a rushing/crackling noise for a few seconds when coming off standby; the sound level increases gradually then fades away completely. - sounds like you can hear the electrons rushing in. . MV kills the noise, channel volumes no effect. Using the scope I chased it down to the junction of C24/R33. Tried swapping out V2, no change. Reflowed the solder joints in that area, no difference. Flexed the board and moved the components with a stick, no extra noise.

Then, last time I turned it on - no noise. No amount of bumping/pushing brings the noise back. I hate to return it to the customer without knowing for sure it's fixed. Any suggestions?

traynor_mkiii_ygl3_3a.pdf

[The Dude]

I would let it cool for a while and retest. It could be something that only happens warming up or after it's been sitting a while.

[Jon Snell]

If the Master Volume reduces the level of noise, the noise is pre the MV and it can be either a phase invertor valve or pre amp valve warming up or an anode load resistor is failing or has gone noisy, like most CC resistors do.

[mhuss]

Thanks for the suggestions - I tried the cool off thing already (overnight), still no noise. The resistors are all carbon film and look to be in decent shape. I should note that someone had already recapped this amp, replacing all the electrolytics, even the cathode bypasses.

[Justin Thomas]

Long shot but a while ago my AB165 Bassman would make a periodic noise that sounded similar; I tried the plate load resistors with no satisfaction; it turned out to be the 220k mixing resistors after the volume controls.

I guess all I have to say is, when the usual suspects fail, look elsewhere. I'm inclined to say it's a resistor, or maybe a resistor connection - just not "the usual suspects." Maybe a connection got knocked loose (or back together in this case) while you were poking & probing elsewhere...

Jusrin

[g1]

It was on the R33 side of C24 coupling cap but not on the V2B tube side? Then I would be suspicious of C24.

[mhuss]

I replaced both the .022 cap and the 100k resistor just for good luck. Thanks all for the suggestions.