Guitar amp warm-up?

[Rhodesplyr]

A younger client asked me whether or not I thought it was worthwhile for him to leave his amp, a '65 Deluxe Reverb Reissue, turned on, in standby mode, for ~an hour before playing a gig, which is what he's been doing.

Not being a guitar player myself, I told him that I really wasn't sure how much difference it made to warm up the amp like that, but I didn't think it should take more than ~10 minutes for an amp like his to be ready to go.

I've played my Hammond/Leslie rigs with just a few minutes warm-up with no apparent deficit in tone, and 6550s take a lot longer to reach full operating temperature than 6V6s.

So I thought I'd ask real guitar players: does it make a difference in tone, or is this one of those superstitious/unexamined habits handed down from guitar player to guitar player?

[cminor9]

Not necessary. In fact leaving the tubes hot for so long without b+ flowing through them is said to be bad. In reality he doesn't even need a standby switch. Check this forum for the thread on standby switches for more info. A lot was said about this topic there.

[Rhodesplyr]

Yes, I already told him not to use the standby switch on this amp. It makes little sense to me to have one on an amp with a 5AR4 rectifier tube.

[Enzo]

It needs less than a minute of warm up, before that it won;t make sound. The standby switch allows you to silence the amp during breaks without having to let it come on again when you return.

When you bias an amp, you should let it sit there running fully powered for 15-20 minutes before doing the adjustment. The amp may drift back and forth some as it warms its little self through. The tubes are perfectly capable of amplifying all this time. But since everyone seems to think bias is rocket surgery, might as well go for the most stable conditions.

The only thing that ever needs an hour to warm up is some bit of lab equipment. In those cases, it is not just the tubes warming up, they radiate heat, as do other parts,and the entire chassis comes up to operating temperature. SUbtle temperature sensitivities in individual components may take a while to settle. Now we are talking very sensitive measuring equipment, not a Deluxe Reverb. And in fact, in those cases, the same rules apply to solid state gear. Must be warmed up a minimum period to ensure consistent measurements. We are talking physics lab stuff here.


Your guitar amp may have a detectable tonal change over the first few minutes of play, and if that small difference matters to your ear, then go ahead and wait it out. But whether or not it is on standby during that period is irrelevant. The tubes will heat up with or without the standby on. It won;t harm the amp or wear it out faster by playing it a minute after the power went on.

[Rhodesplyr]

The only thing that ever needs an hour to warm up is some bit of lab equipment. In those cases, it is not just the tubes warming up, they radiate heat, as do other parts,and the entire chassis comes up to operating temperature. SUbtle temperature sensitivities in individual components may take a while to settle. Now we are talking very sensitive measuring equipment, not a Deluxe Reverb. And in fact, in those cases, the same rules apply to solid state gear. Must be warmed up a minimum period to ensure consistent measurements. We are talking physics lab stuff here.

I might add transistor combo organs and certain analog synths to that list. When I use my Roland Jupiter-6 for something important, I like to give it ~20 minutes to stabilize. At that point, the oscillators seem to figure out where they want to be. Of course, oscillator tuning drift is not applicable to a guitar combo amp...

[big_teee]

I think the same folks that warm up their amps long term are the same guys that warm up their cars for 30 minutes before they go.
I don't have time for Either!
Terry

[Enzo]

I get better sustain from my truck if it warms up well. And it gets awesome dirt.

[jrfrond]

I think that the extended warm-up time from a SONIC standpoint is a bit silly, but what ISN'T silly is not exposing the tubes to yet another thermal cycle. Thermal cycling, and the associated expansion/contraction of components, is a known killer. I actually HIGHLY recommend the use of the standby with to keep the tubes warm during breaks. There's no reason not to. No tube damage will occur.

[km6xz]

There is a "controversy" over standby switches? I guess I miss out on all the latest fads.
Receiving tubes has a controlled heater time for 80% conduction, usually 11 seconds. That was needed back when the All American Five uses series filament wiring so the whole string would drop about 95volts from the mains(no filament or plate transformer) with the rest being dropped by a power resistor.
Power tubes can take longer unless originally designed for consumer systems like the 6V6 and 6L6 which have 11 sec warm up time also.
Directly heated cathodes can be instant on. Many high power tubes are ready for full emission in less than 1/2 second. I have a power amp back home in storage is a home made kludge using 2 3-500Z tubes, with 500 watts of plate dissipation each which generates full power from a cold start in about 1/3 second. In this cases the cathode is the heater so the heater does not have to warm up a cold cathode.
Start up time is not the issue hi-fi tweaks claim but cold down and how it is done have a definite impact on tube life. As John said, thermal cycles matter. If building an amp with a fan, have a thermal or timer keep the fan going for a minute or so after the power has been shut off. I have a SVT here now that I am adding a 3 minute delay on the fan. The owner's tube life will be extended....it is used in a practice studio by a lot of people who have no business using such an amp.

[GregS]

To add to this the power tubes are nowhere near full operating temperature with just the heaters going in standby mode regardless of how long it's left like that. I remember checking this out with 6L6 tubes with one of those temperature measuring devices. In standby mode they would only reach roughly 1/2 the temperature that they would when conducting current - with the amp idling and not even playing through it.

Greg

[Jazz P Bass]

If you consult the old tube datasheets you will note that there is a specified warm up time for each specific tube.
Typically 10-12 seconds.
That is all you need.

[km6xz]

To add to this the power tubes are nowhere near full operating temperature with just the heaters going in standby mode regardless of how long it's left like that. I remember checking this out with 6L6 tubes with one of those temperature measuring devices. In standby mode they would only reach roughly 1/2 the temperature that they would when conducting current - with the amp idling and not even playing through it.

Greg

Yes but do not confuse operational temperature, the temperature at which the tube performs as spec with high plate dissipation that reduces headroom and reduces life of the tube. Because a tube CAN dissipate a certain amount of heat before melting, does not mean that that is its intended operating temperature...unless you like the sag mid performance and replacing tubes more often than they should be. Sure way to make an amp sound better longer, and be more reliable is to help it get rid of useless heat building up on the anode.
Tubes with glass envelopes cool themselves by radiation which is not as efficient as conduction, forced air or fluid. Some pretty nice long lasting tubes used in industrial and communications equipment that use much more efficient cooling techniques would negate the yearly tube replacement, excess heat and vibration induced death power tubes suffer. I posted photos a while ago of an amp I build using small metal exterior anode power tubes, a pair 3cx300's about have the size of a 6550 that coasted at 200w Class A because they have 600 watts of plate dissipation for the pair when in forced air. But I submerged the whole amp circuit including driver board in transparent transformer oil in a glass Pyrex column. With a different transformer, running Class AB, like a guitar amp, it stayed cool at 400 watts. It would do much more if a transformer was available.
If you can get rid of the heat, tubes could be much more powerful than glass tubes are now.