Will This Blow My Amp Up?

[Foolius Maximus]

ok here's the deal - i have a marshall jcm 900 combo amp that i run into my rack using the effects send - it goes through the rack and ends up into a peavey classic 50/50 power amp and out to two 4x12s - nothing gets sent back into the return - here's my question - the combo amp doesn't have speakers - i run the amp without connecting a speaker to it or a load box - the amp stays on standby(meaning i power it on but never turn the standby switch on to hear the amp) because i'm only using the preamp section - will this hurt my amp? and if so is there a cheap load box out there that i can use to prevent any damage - thanx, neddi

[Spivonious]

Wait...you get sound when it's in Standby? That doesn't seem right...

If that is indeed true, then no, your amp is perfectly fine, since all it's doing is running the tube heaters. But running an amp without a load is a good way to blow up the transformer.

[Foolius Maximus]

i freaked out too - i didn't think that was possible but yes, i run the amp while it's on standby

[Spivonious]

Just to be on the safe side, I would connect a speaker to the combo.

[markD]

if the amp is on stand-by, then nothing is going to the power tubes. by coming out of the "send" of the effects loop, yuo are only sending a preamp signal to the rack and power amp. as long as nobody ever flips the stand by the amp will be fine.

[markD]

oh, and until the power section is engaged - hitting the stand-by switch to "on" - the transformers are by-passed.

[SlasZ]

Wait...you get sound when it's in Standby? That doesn't seem right...

If that is indeed true, then no, your amp is perfectly fine, since all it's doing is running the tube heaters. But running an amp without a load is a good way to blow up the transformer.

My Uberschall's preamp also works when in standby. For my apartment I just connect my Bogner's FX send to a small combo amp FX return and I got good sound at low volumes( using a G-Major as volume knob. No need for a load this way.

[Spivonious]

That's good to know. Thanks Mark!

So if the amp is in standby, it's doing more than heating up the tubes.

[markD]

sure. think of an effects send like a "pre-amp out." in fact, that's what peavey and fender call them, or used to anyway. by tapping into the circuit at the preamp out, everything involved with the power section is bypassed. there should be NO effect from the power amp on the signal coming from the effects send.

[toejam]

Strange that the effects send/preamp out is actually giving sound on standby. I'd never heard of that before, but I guess certain amps do, which is pretty neat!

[DonP]

Marshall (and others) F'd up if you get sound in the standby mode, because that means HV is going to the preamp tubes before they are warmed up. Preamp tubes aren't as big a deal as power amp tubes, but still, Marshall should have done it correctly.

Anyho, just pull out the fricken power tube to be on the safe side. Then you are sure nothing will blow up.

[SlasZ]

Marshall (and others) F'd up if you get sound in the standby mode, because that means HV is going to the preamp tubes before they are warmed up. Preamp tubes aren't as big a deal as power amp tubes, but still, Marshall should have done it correctly.

Are you sure about that? If Bogner doesn't warm up the preamp tubes, why should Marshall?

[Firebird V]

It only takes a few seconds for the preamp tubes to heat. Not a big deal. A lot of amps are built this way. I would pull the power tubes just to be safe too or just run a speaker load and then you will have no worries at all ever.

[DonP]

Are you sure about that? If Bogner doesn't warm up the preamp tubes, why should Marshall?

Do you understand what happens to the cathode of a tube when you apply about 300 volts with no heat?

[SlasZ]

Do you understand what happens to the cathode of a tube when you apply about 300 volts with no heat?

I guess I don't, but apparently it's not such a big deal for pre amp tubes?