Popping when amp put on Standby....sometimes

[sonicmojo]

I was wondering if anyone here has experienced random popping when standby is engaged on a tube amp and what may cause this. I have a custom amp on my bench that has an audible "pop" when standby is engaged, but not every time. I've replaced the switch and that didn't help. This amp has no choke. It runs 2 6V6s. It also has the same random pop when I turn off and on my soldering iron on the same power strip. It does not happen every time. Very strange.... Grounding issue? The customer had a complaint on this pop so it is not just my power supply.

[sonicmojo]

The pop does not happen when I have the PI tube out.

[Leo_Gnardo]

How is the standby accomplished on this mystery amp? Not all amps switch off the high voltage. Some merely mute the signal on its way to the output stage. If it's a high voltage off standby, then we have a mystery. If not, the output section is still "live" when in standby and may amplify any signal that comes its way, possibly due to fluctuations in line voltage as you might have when switching your iron on or off. If it's a mute type standby you could convert it & get your customer happy.

[sonicmojo]

It is straight off the rectifier.


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[statorvane]

There was a long running thread a the Metropoulos Amp forum about standby switch squealing/popping with some Metro JTM-45 kits. The problem was noticed with Chinese (Valve Art) KT-66s. I think a work around was to install 5K6 grid resistors on the power tubes. Others tried swapping preamp tubes.

Here is a link to the sticky thread; may be something in there to help you sort this out: http://forum.metropoulos.net/viewtopic.php?f=15&t=12539

[sonicmojo]

Thanks for the link. I’ve spent enough time with this amp. It has a touchy 2 tube tremolo in it that may be part of the scenario and the original builder who I was doing remote debugging for doesn’t want to pursue any more troubleshooting.

[tictac]

I read about rewiring the standby switch to switch the screen B+ supply on and off which puts less stress on the switch too.

Tried it and it works like a charm! No popping noises and amp is silent when in standby.... Lots of stanby switch replacements could have been avoided if Fender had does it this way...

TT

[RockinRocket]

Id advise not using HT standby switches (or simply leaving on play) with tube rectifiers. It can take them out or worse.

My amps I built pop as well when using rectifiers but never on a diode build.