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If tube amp is left on, but not playing........

If a tube amp is left on , but not playing, is the tube still wearing out? If you think of the tube as a valve, and no electrons are moving through it, it would seem that there is little to no wear on the tube. This is a significant question for me, I am considering a SET for a system that will be used by my family. My wife has never shut off a light in her lifetime, and will not turn off the amp when not in use. (Those of you who respond with suggestions on how to change my wife's behavior have never been married!!) thank you......Mark
mythtrip

Showing 3 responses by herman

herman
2,277 posts
 
I don't think turning off B+ will help much if the filament is on. The filament will still be cooking away and shortening the life of the tube.
herman
2,277 posts
 
Hi GS556, I am afraid you are wrong on all counts. A transistor and a tube operate in the same fashion when used in an audio circuit. It is true that a transistor will be off with no signal or bias applied to the base, and a tube will be on with no signal or bias applied to the grid, but they are never used in an audio circuit without some bias applied.

How much current they pass at certain signal levels depends on how they are configured. Class AB push-pull amps, whether tube or transistor, pass a small amount of current at idle and more when a signal is applied. Class A amps, whether tube or transistor, pass approximately half of the maximum current at idle and then this amount varies up and down with the applied signal.

The reason you should never power up a tube amp with no speakers hooked up has to do with how the output transformer operates, not how the tube operates. Energy is transferred from the primary of the transformer to the secondary by magnetic fields. When the expanding and contracting magnetic fields created by currents in the primary windings cut through the secondary windings, they induce current to flow through the speaker. Without a speaker hooked up, this energy has no where to go but back through the transformer primary where it induces a large voltage across the output tubes. This can cause the tubes to arc and damage them.
herman
2,277 posts
 
Dear Mr. Ghost Rider,

I cannot disagree. Your point about thermal shock is very real. That is why light bulbs almost always burn out when first turned on.

I think it all depends on how much the equipment is used. If you play your amps only on the weekends, then it probably makes no sense to leave them on all the time. If you listen all day long every day then maybe you should leave them on all the time. I have never heard a definitive answer, but perhaps someone here can site a study that will tell us for sure.

I turn my amps off when I am not at home or I am sleeping. I am more worried about fire than consumption of electricity or tubes though.
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