Noobish Question about Heads not being plugged into cabs...

Drow Swordsman · #1 11-26-2007, 04:48 PM

Okay, so I've heard many a time that you can damage the tubes (and the amp circuity itself), if you leave an amp head on for awhile without having it plugged into a cab.

Here are my two questions:

1) How long does it take before damage can occur?

and

2) Does damage still occur if the head is on but left on standby while not being plugged into a cab?

These questions have been eating at me so I just decided to ask today.

Thanks!

jb4674 · #2 11-26-2007, 05:07 PM

I don't think you can damage a head by plugging it in without a cab attached to it. First of all, what exactly would damage the head? Secondly, the standby switch (if present) is there for a reason, and that is to allow the head to be put into standby mode. With that being said, it doesn't mean that you shuold leave the head in standby for days. Generally, I'll put my amp on standby if I'm going to do something like washing a few dishes, or switching clothes from the washer to dryer, etc. If you're going to be away from your amp for an hour, then I would recommend you turn it off altogether.

I hope this helps.

Jimmy

shogun · #3 11-26-2007, 06:26 PM

im sure someone who knows what they are talking about (not me) will answer this, but I have also heard that it can damage an amp to be producing power, but not putting it anywheres.. I would definitely plug my cab in before even having it on standby, thats just common sense.

tobe · #4 11-26-2007, 06:30 PM

Quote:

Originally Posted by shogun

im sure someone who knows what they are talking about (not me) will answer this, but I have also heard that it can damage an amp to be producing power, but not putting it anywheres.. I would definitely plug my cab in before even having it on standby, thats just common sense.

Yes, if you do not have your amp connected to some kind of load, whether be speakers, or a "dummy load" you can, and most likely will damage your tube amp. It puts a ton of stress on the amp to be producing a load that is not dissipated somehow. Standy, does just what it means. The amp is warm and ready, but not yet producing any power. Thus, while I wouldn't recommend it, you could not have a cabinet attached and it would be ok.

Racerx2k · #5 11-26-2007, 06:35 PM

Yes, people have fried their innards, because they had a tube amp on, without a cabinet. I, however, was never sure if it was okay while in standby, or not. I always err on the safe side, and turn off, anyway. What's a couple seconds, compared to a toasted tranny?

andy7jem · #6 11-26-2007, 06:46 PM

Quote:

Originally Posted by Racerx2k

What's a couple seconds, compared to a toasted tranny?

Oh boy.....i'm gonna leave this one to Cid

jemplayer55 · #7 11-26-2007, 06:51 PM

It is generally not good to run a tube amp with no speaker load as the output transformer can heat up excessively. (IN OTHER WORDS.... DON'T DO IT!) This will happen quickly and will damage the transformer. The reason is..... in an unloaded state it can generate quite large voltages within the transformer windings, breaking down the insulation and cause internal shorting. Even when firing up a fresh amp build you always do it with a speaker load.

Even in the standby mode there needs to be a speaker load on the output transformer. The standby switch is used to turn off the high voltage to the amplifier's tubes, not to the transformer. This only applies to tube/valve type amps. Solid state is a whole different ball game.

jemplayer55 · #8 11-26-2007, 07:06 PM

Quote:

Originally Posted by tobe

Standby, does just what it means. The amp is warm and ready, but not yet producing any power.

This is only partially true.... as soon as a tube amp is turned on it is receiving power to the output transformer. The voltage (signal) to the power tubes is all that is cut by the standby switch.

Quote:

Originally Posted by tobe

Thus, while I wouldn't recommend it, you could not have a cabinet attached and it would be ok.

This part is bad advice and must have been based on assumption.

Racerx2k · #9 11-26-2007, 08:04 PM

Quote:

Originally Posted by andy7jem

Oh boy.....i'm gonna leave this one to Cid

Okay, let me specify: transFORMER! Wait.....now that sounds like someone who ONCE was a tranny.....Okay, I give up........

Drow Swordsman · #10 11-26-2007, 10:35 PM

Oh goodness, thank you for the advice.

I've said this because I've been a/bing two different heads to compare them and for awhile I left them on standby while I was playing the other.

I now take it this was a bad idea.

So here's a new question: Will there be any damage I can't see? Or, if my transformer isn't blown up, is everything fine and as long as I do it again I don't have to worry about it??

jemplayer55 · #11 11-26-2007, 11:15 PM

^^^^ If it's still working it should be fine. But there are no guarantees on that. The damage and how quickly it occurs is dependent on several things..... type of construction, including things like the layers of insulation between windings, how thick they are, and like a pickup how it was potted to seal it up. So chances are you won't see any damage. Especially if the transformer has metal "bells" that enclose it. If it has exposed coils like some old amps... you'd get pooling of the sealant. For example if waxed paper was used and it got overheated.

This site might help explain transformers for amps. See the FAQ's

http://www.mercurymagnetics.com/pages/mainframe.htm

Paul_R · #12 11-26-2007, 11:28 PM

Applicable lesson: When your shopping on 3bay for amps and see these kind of pics, you may want to ask how the amp was treated.

Nice looking...

and not connected to a cab. OUCH!

Hope the photo shoot didn't take too long.

rgr · #13 11-27-2007, 12:42 AM

Quote:

Originally Posted by jemplayer55

This is only partially true.... as soon as a tube amp is turned on it is receiving power to the output transformer. The voltage (signal) to the power tubes is all that is cut by the standby switch.

Nope, the plate voltage is cut by the standy switch. When in standby, the heaters are powered to warm up the tubes. Some amps may have plate voltage on the preamp tubes in standby, you can find out by seeing if there is a signal on the effects loop send. If there is a signal coming out of it, the preamp tubes have plate voltage. But, there is no plate voltage on the power tubes, therefore, they can't amplify, hence, nothing is going through the output transformer. It won't hurt the amp to be powered on, but in standby with no cabinet plugged into it. It also won't hurt the amp to be on and out of standby with no cabinet IF there is no signal being fed into the amp, as soon as you start giving it a signal to amplify, with no load to dump into, it's like holding your nose while blowing out it as hard as you can, eventually your eyes will pop out (well, not exactly, but it's the best analogy I could think of).

Vim Fuego · #14 11-27-2007, 05:41 AM

Just to add to the confusion, What rgr says is right except:

"It also won't hurt the amp to be on and out of standby with no cabinet IF there is no signal being fed into the amp"

If the amp is class A or AB (like a Vox AC30) then there is always current going through the transformer when the amp is on and out of standby. (I once set up my AC30 near a wall of tv screens and the magnetic field from the output transformer made the nearest screens change colour, it wasn't the mains transformer doing it!)
My 2p worth unless you're sure the standby switch disconnects the HT from the power tube correctly then ALWAYS have the correct load connected to the amp when it's on.

rgr · #15 11-27-2007, 01:24 PM

Agreed, there can be a small amount of current going through the transformer when it is on and out of standby, probably not enough to do any damage for a short period of time, if you left it on for days, it might do some damage. This signal is most likely just circuit noise being amplified, so if your amp is set super clean, there probably won't be much if any, if the pre is cranked, you'll have more noise. But, I agree, I wouldn't recommend doing it. In fact, it is a better mindset to always have a load plugged in if the amp is plugged in. I do flip my amp on standby and switch cabs, that won't hurt it a bit, as long as you plug a cab back in.