Amp on Standby damaged by not having speaker connected?

[Tonefish]

Can an amp on standby be damaged by warming it up without a speaker connected?

I have never done this, but I wouldn't expect it would matter. Anyone know with certainty?

[Blue Strat]

No problem with no load and the amp on standby because the amp isn't actually operating.

[bob-i]

Actually you'd have to play with the amp on, speakers disconnected for some time to damage an OT.

[John Phillips]

Actually you'd have to play with the amp on, speakers disconnected for some time to damage an OT.
Not true, you can damage it instantly. It's not a heating issue, it's to do with flyback voltage, and if it exceeds the insulation breakdown voltage the transformer will arc - it doesn't matter how long it's been on for, you could do it on the first loud sound you put through it, if you're unlucky.

[Tonefish]

No problem with no load and the amp on standby because the amp isn't actually operating.

OK..that's what I thought...thanks!!

[slide man]

John or anybody else for that matter. I was recently working on an amp and I unkowingly turned it on and tryed to play it with out a load for probably at least thirty seconds before I figured out why I wasn't getting any sound. When I finally did figure ou what was going on I cut the amp off plugged in the speaker and the amp cut on. However the amp is really generating a lot of noise /hum when I am pluged into it. It really isn't humming to any great degree or more than usuall when nothing is plugged in. Does this sound like I damaged the transformer? Or maybe something else since I was working on it when this stuff started.

Slide Man

[John Phillips]

No, if it's not humming when nothing is plugged in, it doesn't sound like the transformer. Although you can damage one instantly, you can also get away with it for ages, or indefinitely - it just depends on the particular transformer and whether its insulation will hold up.

If it only hums when something is plugged in - and assuming the input jack does not have a grounding switch which operates later in the amp circuit - I would check the jack ground connection first, and if not that it's likely to be what you've got plugged into it, not the amp.

[slide man]

Thanks John. You know come to think of it it does seem to sound like a ground type hum. It really reminds me of the hum I would get when I tried to use a Plex in certain venues.

Slide Man

[gtr777]

I can tell you from experiance that my SLO100 's fude blew quite quickly when I powered it up by accident without the cab hooked up...

[John Phillips]

What actually arced? Transformer or tube/socket? If replacing the fuse and connecting the cab made it work, most likely a tube.

BTW, is the SLO unstable with no load? The Mesa Dual Rectifier (quite similar amp) is, and will self-oscillate at full power if you turn on the standby without a speaker connected, even if there's no signal present. That will cause something to arc fairly quickly probably...

[Doug H]

How long you can run an amp unloaded depends on the amp. I've got a single-ended amp I built that I inadvertently ran for 15min unloaded one time- no problems. I wouldn't suggest trying it though...