Vox AC30's: to use standby switch or not?

[Gutch220]

I'm hearing a lot of comments regarding the fact that it is possible to cause a 700v voltage spike in your AC30 if you use the standby switch. This can potentially cause damage to the rectifier tube, output transformer, filters caps, and so on. So what is the true answer? Use the standby like normal, or not use it? Why would Vox create a standby switch if it can cause serious damage?
I e-mailed Vox and am awaiting a response. I am interested to hear what everyones views/experiences were with this.

[P-Dawg]

I'm hearing a lot of comments regarding the fact that it is possible to cause a 700v voltage spike in your AC30 if you use the standby switch. This can potentially cause damage to the rectifier tube, output transformer, filters caps, and so on. So what is the true answer? Use the standby like normal, or not use it? Why would Vox create a standby switch if it can cause serious damage?
I e-mailed Vox and am awaiting a response. I am interested to hear what everyones views/experiences were with this.

There's a pretty good technical discussion here on the subject. When you think about it, the articulated reason for a standby is to keep your tube filaments hot while disconnecting high voltage from the circuit. This, it is said, is a good thing. I can also see some rationale for one where you have solid state rectification.
Howevah, when you have an indirectly heated rectifier like the GZ34, before you get any B+ your power tubes are up to temp anyway because of the slow warmup time. So the 'protect the power tubes' argument goes away.

Think about all the cheap tube amps you've seen that have lived long and happy lives without standby switches. Did anything bad happen to them?

So....after reading the excellently articulated reasons for avoiding using standby on the AC30CC I decided it was good enough for me and I swore off.

Maybe we need a 12 Step Program here......"Hi, I'm Robert and I use standby switches."

[harborcoat26]

I'm hearing a lot of comments...

I don't know if you saw all the comments here, but here they are if you are interested:
viewtopic.php?f=2&t=75667

Long story short: don't use standby unless you are using a SS like the Weber Copper Cap - then it is okay!

[Gutch220]

I think from now on I won't use the standby switch at all as well.
I just flipped the power switch on with the standby already on and the standby light took several seconds to light up so I assume this is the amp powering up slowly.

[Mayhawk]

NOT.

[iamthenoise]

How about turning the amp off? use the standby first? does it matter?


also, i grew up being taught that when powering down your tube amp, you should then flip on the standby back on AFTER the power is off, to discharge the caps. is this a poorly learned bullsh*t habit, or is it legit?

[P-Dawg]

How about turning the amp off? use the standby first? does it matter?


also, i grew up being taught that when powering down your tube amp, you should then flip on the standby back on AFTER the power is off, to discharge the caps. is this a poorly learned bullsh*t habit, or is it legit?

Depends on the circuit topology but in most cases there's enough leakage somewhere to bleed the filter capacitors down in a few minutes. If you flip the standby switch to the ON position, of course you are opening up another path to ground through the B+ rail if there's some leakage there. Some amps have a bleeder resistance built in for just that purpose.

Of course, when servicing your amp the first thing to do on opening your cabinet is to take a test lead with a 1 meg resistor cut into it, clip it to the plate lead of the first preamp tube and then to ground and leave it there while you're working on a cold chassis.