Amp loudly pops when switched from standby to on

[archaos]

Yes, that's actually what one of my AC30 does. Besides that's rather a loud heart-attack giving noise not really a pop, though the amps works perfectly. Any ideas  ? Cold solder joint, out tubes...?

Thanks for tips, suggestions.

[plexi50]

I would check your power tubes on a tester real fast before turning it on again. You need the schematic to check for any odd wiring issues in the standby circuit

New tubes? Dont mean much these days. Get them tested. Hold one of the power tubes in your fingers horizontal. Flick the tube with your finger as you rotate it and look for any shiny or white flakes floating around in the glass. If so this could be a tube that has shorted and is bad news. Dont gamble and loose your OT. Do you have a rectifier tube in your amplifier?

Ive never seen cows on the beach before. What do they eat? Sandfleas? No wonder those spare ribs have no meat on them

[billcreller]

That subject was discussed here a couple of years back, and of course I don't remember the details

[Merlin]

The new standby switch was a blunder on Vox's part (the original AC30 never had one) and has lead to a lot of GZ34s going south. Depending on which version of the AC30 you have, there may be a resistor soldered in parallel with the switch (there certainly should be if you want your GZ34 to last reliably.

The popping sound can be reduced by adding a rectifier diode (e.g., 1N4007) immediately after the switch, before the reservoir cap. This will keep pure DC off the switch and reduce switch arcing.

[archaos]

I would check your power tubes on a tester real fast before turning it on again. You need the schematic to check for any odd wiring issues in the standby circuit

OK I've checked the tubes & the schematic this afternoon. My amp is almost exactly built like the Hoffman AC30 (see attachement) excepted it has a standby switch & & .5A fast-blow fuse between the GZ34 & the 1st filter cap. I haven't noticed oddities concerning the wiring.

New tubes? Dont mean much these days. Get them tested. Hold one of the power tubes in your fingers horizontal. Flick the tube with your finger as you rotate it and look for any shiny or white flakes floating around in the glass. If so this could be a tube that has shorted and is bad news. Dont gamble and loose your OT.

The power tubes, JJ are not new ones ; I've used them for 2 years, but no flakes appeared on them. Nonetheless, I got no noise/pop with the tubes pulled.  ...

Ive never seen cows on the beach before. What do they eat? Sandfleas? No wonder those spare ribs have no meat on them

Those sunny cows are in Corsica where they are free to get some tan on the beach, & then can eat some grass in the mountains as far as the island is very green.

The new standby switch was a blunder on Vox's part (the original AC30 never had one) and has lead to a lot of GZ34s going south. Depending on which version of the AC30 you have, there may be a resistor soldered in parallel with the switch (there certainly should be if you want your GZ34 to last reliably.

The popping sound can be reduced by adding a rectifier diode (e.g., 1N4007) immediately after the switch, before the reservoir cap. This will keep pure DC off the switch and reduce switch arcing.

Never heard about that resistor before, but that's true my amp which was formerly a 93 Korg/Marshall reissue had a terribly bad standby switch wiring (see attachment) in so far as it didn't allow the GZ34 filaments to heat up before switching the amp on. Thus the GZ34 life was shortened.
Finally, what do you recommend guys ? Should I add some components (res./diode...) or should I swap the tubes ?

[jhadhar65]

>Finally, what do you recommend guys ?

Stop turning the standby switch off.  It doesn't take that long to warm up.

[archaos]

there is your problem

jj's

get rid of them.

Why ?

[Merlin]

Why ?

The popping has nothing to do with the valve types. Ampcabinets is just being facetious.

[archaos]

Why ?

The popping has nothing to do with the valve types. Ampcabinets is just being facetious.

I thought he had a grudge against Czech... 

[Fresh_Start]

The new standby switch was a blunder on Vox's part (the original AC30 never had one) and has lead to a lot of GZ34s going south. Depending on which version of the AC30 you have, there may be a resistor soldered in parallel with the switch (there certainly should be if you want your GZ34 to last reliably.

The popping sound can be reduced by adding a rectifier diode (e.g., 1N4007) immediately after the switch, before the reservoir cap. This will keep pure DC off the switch and reduce switch arcing.

I don't doubt that this setup is a problem but don't understand WHY.  On the Valve Wizard site, it says that having a DP/DT switch between the PT secondary and the rectifier is the BEST way to wire a standby switch:
http://www.freewebs.com/valvewizard1/standby.html

That looks exactly like the AC-30 schematic which archaos posted.

What are the conditions which endanger a rectifier tube such as a GZ34?

Thanks for your thoughts,

Chip

[Merlin]

I don't doubt that this setup is a problem but don't understand WHY.  On the Valve Wizard site, it says that
What are the conditions which endanger a rectifier tube such as a GZ34?

Because that is a mistake on my part- I wrote that page a long time ago and was concentrating on switch ratings and popping sounds, rather than recto life. I will update it.

In short, tube rectifiers do not like to be "hot switched". That is, they don't like it when you let them warm up and then throw the switch so they suddenly have to charge the reservoir cap. This can quickly lead to arcing, especially with the new GZ34s. If you really want a standby switch in an amp with a tube recto (why?) then it should be placed after the reservoir cap, or else it should have a resistor connected in parallel with the switch, so the cap can charge at the same time as the tube warms up.

[archaos]

...or else it should have a resistor connected in parallel with the switch, so the cap can charge at the same time as the tube warms up.

...& that's what I'll do with a 56K 2W resistor, thanks. 

[Fresh_Start]

OK, does the advice on that Valve Wizard page apply if I am using solid state diode rectifiers? 

IOW, is there any advantage to using a DP/DT switch between the PT secondary and the rectifier diodes vs. the traditional SP/ST switch between the rectifiers and the reservoir cap?

I am guessing that the advantage of the DP/DT switch before the rectifier diodes would be keeping DC off the switch and reducing the chance of arcing.  However, that is just a guess at this point.

Respectfully,

Chip

[Merlin]

OK, does the advice on that Valve Wizard page apply if I am using solid state diode rectifiers? 

With an SS rectifier you can put the switch anywhere you like, although the switch will live a happier life in the AC part of the circuit, rather than after the rectifier in the DC part of the circuit. Popping is also less likely if the switch is in the AC part of the circuit.

Better still, don't bother with a standby switch; it doesn't do anything particularly useful.

[Fresh_Start]

Better still, don't bother with a standby switch; it doesn't do anything particularly useful.

I won't argue about that statement; however, in my very limited experience customers think they need a standby switch.  They seem to believe that "better" amps have one, whether it does anything useful or not.

Chip

[punkykatt]

Better still, don't bother with a standby switch; it doesn't do anything particularly useful.

Comes in handy for me when switching guitars on stage. We mic all the instruments. Dont want that nasty noise going through the main PA.  I also disconnect from the amp to tune the guitars through my old fashion tuner. 

[jhadhar65]

>I also disconnect from the amp to tune the guitars through my old fashion tuner.

Do what works best for you.  I do almost zero stage work anymore - only when they can't find anyone else will people I know consider dragging me out of the mothballs.

Still, I've been using a BOSS TU-2 pedal tuner for years and I'll typically kick that into mute tuning mode instead of flipping a standby when I need to yank a plug.  Otherwise, instead of a usual stand by condition, I just kill the amp.

Back to archaos... I have standby switches on all of the amps I have, but they all stay in the "ON" position all the time - I don't use them.  I also don't use standby for startup or shutdown.  Again, though, do what works for you.