Played tube amp without speaker connected.

[trojax]

Hi, I was recently working on finding a way to get my Bugera V22 amp signal to a direct box To do this I was running from my effects loop straight to the box. While I was doing this, I needed a way to silence the speaker because the venue I am playing does not want any sound coming from the stage, only the PA. In my Ignorance, I disconnected the speaker and thought I had found my solution. I played with it like this for possibly 1-2 hrs total, though this was spread throughout a couple days. I then learned of the great risks involved in doing this while I was researching direct boxes. The amp still works, but I am worried that some damage may have been done. The clean channel sounds fine, and I think the lead channel is fine as well, but there may be some change there. I may just be paranoid, but I would like to be sure that things are ok with it.

Could anyone tell me if their are any easily recognizable signs that an output transformer is damaged, or any other part of the power section? I want to find out if something is wrong soon because the amp is a recent purchase.

Thanks for any help.

[pdf64]

The key issue is insulation damage on the output transformer primary circuit.
The best check for this is to play the amp loud; if it will cope with full power and being pushed into power amp overdrive (ideally into a speaker) without crackling or cutting out, then it should be ok.
Pete.

[trojax]

Well I played the amp, pushing it well into its natural overdrive ranges. Ran the lead channel throughout its gain range. Maxed out the master volume even. It sounds.....well it sounds wonderful. I think I may have dodged a bullet, but I really do not understand how. During the time I was playing it w/o the speaker I was running it clean channel full master half for part of the time. There was no smoke or strange smells, and honestly I would have kept going had I not started shopping around for some specialized DI boxes. I honestly don't see how, according to all the cases of damaged amps, mine could have gotten away scot-free. Any Ideas. Think I should check anything else? Maybe these stock Bugera transformers are better than some have said.

[txstrat]

Maybe these stock Bugera transformers are better than some have said.

The transformers are built like every other. I would fear they will eventually be damaged when played with no speaker load.
Maybe there is some sort of protecting circuit around the speaker jack, like a (high wattage small resistance) resistor across the speaker out. This will keep the amp -sort of- save to a degree, although I wouldn't try to do it again with no speaker load. OT once damaged it's history.

[trojax]

Yeah, I was thinking/hoping this might be the case. Wish Bugera would give out a wiring diagram for it.

[Enzo]

There is nothing special about it. DOing that to an amp COULD cause damage, but that doesn't mean it will ALWAYS damage the amp immediately. If it works, then in all likelihood the amp is fine.

As to Lead channel versus clean channel, NOTHING about the output tranformer will affect only one of those channels and not the other.

[Intergalactic Tourister]

If you were running from your effects loop straight to the box... why didn't you just unplug the effects loop going back into the power amp? That would seem less damaging.

[trojax]

It was unplugged. A dry signal still goes through if only one side is connected.

[Intergalactic Tourister]

Ok. So the effects loop isn't like a "preamp out/power amp in." I thought the signal goes through the preamp>preamp out>effects loop>power amp in.

I guess what I failed to mention is the need for a cable plug to be plugged into the "power amp in" only to lift the tab on the jack to prevent the signal from going though the power amp.

An amp turned on with no signal seems better (and I don't know how much better really) than an amp turned on having a signal.

I don't know a lot about direct boxes, hint my questions. Thanks for letting me know.

[trojax]

Yeah I was thinking about trying that. I wont need to for a while though, till a similar gig comes along.

[Intergalactic Tourister]

Maybe using only a tube preamp in that situation.

I use a preamp only sometimes. At least you won't have to lug a bigass cabinet around for nothing.

But I too can't tell you the extend of damage, if any, was caused. Sorry.

[R.G.]

As usual, Enzo is correct in depth.

Playing without a speaker is not certain death to the OT, necessarily; it depends on what the amp does when there is no speaker on it. Some amps go into nonlinear fits and create voltage spikes that kill the OT. Some amps don't care that much. Without killing a few amps, there's no way to tell what it will do, or *when* it will do it. So the best advice is "don't do that", and you'll never raise the question.

If it plays and works fine now, you got away with it. OTs mostly don't degrade subtlely. If it doesn't sound sick and limping, about to die, then it most likely isn't.

So go ye and sin no more. Make yourself a dummy speaker, a BFR (Big Freakin' Resistor) with a cord to plug into the speaker jack when you pull the speaker. This needs to take the maximum power without burning out, but it can be arranged. And you can often find surplus resistors to make these up in adequate power for a few bucks. You can series/parallel resistors to get there. With an amp rated at only 22W, it's not too difficult. For instance, look here:Power Resistors | AllElectronics.com. You find 1 ohm/25W for $2.00 each (4 in series = 4 ohm/100W); 2 ohm/10W for $0.50 (Four in series = 8 ohm/40W eight in series/parallel = 4 ohm/80W); 12 ohm/5W @ $0.33 (3 in parallel = 4 ohm/15W; 6 in series/parallel = 8 ohm/30W); 16ohm/5W; 50 ohm/25W @$1.00 (six in parallel = 8.3 ohm 150W). You see where this goes.