[richidoo]

Is the rate of electron exhaustion in a tube proportional to the power dissipated, or is it a constant wear rate regardless of signal output?

or, to put it another way....

If I leave my tube amps on when there is no music playing, am I burning them up just as fast as when I am playing loud music?

And presuming the latter is correct, a followup, if I may?   If the wear rate is less without signal, then is the wear rate proportional to the signal (no signal = no wear), or is there still a minimum amount of life wasting away just by being turned on?
Thanks
Rich

[JoshK]

Its not quite that simple, because it depends on the class of operation of the amp.  If it is honest to goodness, no marketing fluff, class A then actually the greatest tube wear is when there is no signal.  Tubes are biased for a constant dissipation in class A regardless of signal or not.  When signal is applied it can actually steal some of the bias current away from the tube, so under signal the tube can be dissipating slightly less.  I am not sure the difference is all that meaningful in terms of life, but that is the facts.

In class A/B, the tubes are dissipating their bias current constantly.  The bias current determines how much into class A they are biased, after which operation can go into class B (or even class A2, or B2, to complicate it even more).

[*Scotty*]

The filament current is a constant wear factor as long as the tube is turned on. The cathode has a certain number electrons and sooner or later they will be exhausted,exactly when this will happen is subject to a lot of variables, many of which are not under the users control. The above info was taken from the Manley Labs website and owners manual. If the output stage is biased heavily into class A operation than it will burn almost same the amount at idle as it does at full power,these devices are also known as tube based space heaters with all that implies for your power bill. More information on tube life can be found on the Manley Labs website.  http://www.manleylabs.com/containerpages/snapper.html   From what I can gather from the web, if you have enough money to regularly re-tube the output stage you might as well leave it on all the time, the only down side I can see is the power bill and potential for system damage if your preamp or power amp mis-behave when they see a power bump or outage.
Scotty

[richidoo]

Interesting... Thanks Josh. I forgot about class A.

Funny Scotty, because I have Manley Snappers! Thanks for the insights.

I am just curious about the physics inside those magic glass bottles.
Thanks!!
Rich

[*Scotty*]

 richidoo, Here is a link to another site with some information on tube life and amplifier designs.    http://www.mosweb.com/knowledgebase/tp4.htm
Scotty

[richidoo]

Nice page Scotty - I liked the blurb about OTLs... 

Is it easy to figure out how many watts into class A my amp is biased? Is there a simple formula? 30ma x 4 tubes, 570V plate, 170W idle dissipation including signal tubes and heaters.
Thanks a lot.
Rich

[Steve]

"If properly designed, either circuit can offer improved performance over an ordinary resistor-loaded tube stage."

I do question this sentence, but otherwise a nice article.