Proper Way To Turn On Shut Down A Tube Amp

Turn the amp on for a few mins in standby, then hit the standby switch; play bass, put it back in standby for a few mins when done, then turn off power. Repeat as necessary...

+1

A little more explanation in case you want to know what’s really going on in there:

When an amp is powered up and in standby mode, electricity is flowing to the heater filaments only; the rest of the circuit is dark. This allows the tubes to come up to operating temperature before full voltage is applied to the tubes. Pre-heating the tubes reduces cathode stripping and extends tube life. You can preheat your tubes for as long as you like but there’s probably not much benefit beyond one minute. I’ve known old tube radio guys who say 30 seconds is plenty.

You can turn the amp off any way you want. There’s really no advantage in “post-heating” the tubes.

I've read that it's a good idea to turn them off while not in stand-by...something about caps I think; but I really don't know.

you can think of turning on the power as firing up the engine, and taking it off standby as slamming it into gear. which would you do first?

+1 to the turnoff order not mattering (unless you're getting ready to open up the amp to work on it).

There was a thread about this about 10 to 12 months back. The consensus was that the turn on sequence was as described - turn on, wait at least 30 s, then release standby. OK, no problem.

However, I was surprised to hear people say that shut down should occur immediately, with the amp on, and that turning it off before hitting standby was important for some of the older amps, but not others, due to capacitive discharge.

And that was counter to everything I've ever experienced. I used tube amps exclusively for most of my early years, because that's really all there was - Fender Bassmans and Sunn Model T's (never got an SVT). We ALWAYS put them in standby for 10 minutes +/- at the end of the gig until they cooled down. Every guitar player I've ever played with still does this same thing.

So, after that thread I tried feeling the heat coming off the back of the amp with and without putting the amp in standby. These days, I'm using a TE Hexavalve. Result: No question that the amp cools down way faster running in standby.

I refuse to believe that switching the circuit off while the tubes are hot is a great idea. So, I'm going to keep putting the amp in standby for 10 minutes or so to let it cool down. You guys can post all you want to the contrary. Yes, I realize standby still sends an idle current to the tubes, yadda yadda. They still cool down faster in standby with the fan running. IME.

walterw said:

+1 to the turnoff order not mattering (unless you're getting ready to open up the amp to work on it).

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That's what it was...turn it off while not in stand-by to help discharge the caps before working on it. Thanks.

I too have felt that shut down by going to stand by for a few minutes allows the tubes to cool a bit before the fan is turned off (SVT).

My assumtion being that allowing the fan to run with just the filament heaters on allows the tubes to cool off some and is better than a hot shut down.

Question is:
* Is this assumption correct?
* Does it really matter?

The reason you are noticing it cool off faster when in standby is due to the fan running at this time, where as if you turn if off the fan no longer runs.

I gig 30+ year old amps and am religous about the 30+ second power up. Never did anything special about power off, and have never had any issues as a result. I guess I can see the benefit of keeping a fan running for a few minutes, though - but only my SVT even has a fan.

Tube amps are a lot tougher than most people give them credit for.

nysbob said:

I gig 30+ year old amps and am religous about the 30+ second power up. Never did anything special about power off, and have never had any issues as a result. I guess I can see the benefit of keeping a fan running for a few minutes, though - but only my SVT even has a fan.

Tube amps are a lot tougher than most people give them credit for.

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Well, the amps are mostly built like brick privys. That's not the issue. The question is what effect there is on the tubes. My impression is that you want to avoid thermal shock to the tubes and you want to cool them down before moving them (in the amp, of course). For both of those reasons, I prefer the standby for several minutes as stated earlier. JMO.

30 seconds to a minute before turning the standby makes good sense; that'll protect against cathode stripping. As far as shutdown, on an amp with no fan, just kill the power. If there is a fan involved, I'd then do the standby thing.

For those of us who gig tubes in a northern climate, we also have to let things settle before powering up and loading out on those wonderful below zero nights.

I like to put in stand-by, before turning the power off. This guarantees the amp will already be in stand-by the next time I turn it on.

K2000 said:

I like to put in stand-by, before turning the power off. This guarantees the amp will already be in stand-by the next time I turn it on.

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Ya, that's all I do. I'm with Bob...tube amps aren't nearly as delicate as people make them out to be. The standby while powering on is important, but I don't see any advantage to letting it cool down in standby. I do, however, see a great advantage to letting it cool down a few minutes before you move it. I'm not a tech so I could be all wet about that, but most of my tubes last years and years, so what can I tell you?

Here's a thread I started on "Do's and Don't for Tube Amps"

http://www.talkbass.com/forum/showthread.php?t=501300

bucephylus said:

There was a thread about this about 10 to 12 months back. The consensus was that the turn on sequence was as described - turn on, wait at least 30 s, then release standby. OK, no problem.

However, I was surprised to hear people say that shut down should occur immediately, with the amp on, and that turning it off before hitting standby was important for some of the older amps, but not others, due to capacitive discharge.

And that was counter to everything I've ever experienced. I used tube amps exclusively for most of my early years, because that's really all there was - Fender Bassmans and Sunn Model T's (never got an SVT). We ALWAYS put them in standby for 10 minutes +/- at the end of the gig until they cooled down. Every guitar player I've ever played with still does this same thing.

So, after that thread I tried feeling the heat coming off the back of the amp with and without putting the amp in standby. These days, I'm using a TE Hexavalve. Result: No question that the amp cools down way faster running in standby.

I refuse to believe that switching the circuit off while the tubes are hot is a great idea. So, I'm going to keep putting the amp in standby for 10 minutes or so to let it cool down. You guys can post all you want to the contrary. Yes, I realize standby still sends an idle current to the tubes, yadda yadda. They still cool down faster in standby with the fan running. IME.

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You do realize that the primary source of heat in a vacuum tube remains operational in standby mode, right? The amp chassis might cool faster in standby because all of the other heat producing elements in the amp (i.e power resistors, HV transformer, rectifiers, etc) get shut down while the fan remains on. But the tubes themselves will definitely cool faster with the power shut down entirely. The filament is by far the largest contributor to the heat produced by a tube especially under idle conditions. It's simple physics.

That being said, I'm not sure that cooling things down faster is necessarily a desirable thing anyway. However, in the large scheme of things it really doesn't matter whether you power the amp down entirely or put it in standby. Doing one or the other has no appreciable affect on tube life.

I was involved in the design of a hifi tube amp using 300Bs and 6SN7s and at the prototyping stage we were trying to decide if a standby circuit was necessary so we built a prototype with standby and one without. I designed a soft-start circuit for the non-standby version that slowly ramped the HV up so that the tubes were heated adequately by the time the HV reached its full value. We power cycled the things 1000 times each, putting the standby-equipped on in standby for a few minutes on power up and power down. The result was that not using standby had zero effect on the tubes, so the production amp does not have a standby switch. The few tube failures any of our customers have had with these amps have been categorically attributable to defective-from-the-factory tubes.

The long and short of it is that there's no actual reason to leave your amp on standby for any period of time when you shut it down. And not really any reason to not do it, though there is a school of thought that maintains that it is not good for tubes to be left for long periods of time with just the filaments operational.

Oh, and the critical filter caps will drain at the same rate whether you put the amp in standby or not.



FWIW, I flick my SVT to standby before turning it off, just so it will be in standby when I power it up the next time.