stupid tube question of the day

6bq5 -- I can't speak to other tube makes or gear, but in the case of ARC, the factory recommends that power tubes in more current models, such as 6550Cs, be replaced every 2000 hours. These particluar tubes bias at 65 mV. ARC has replaced the 6550C in some amps with a new tube, the KT-120, which is supposed to be more robust. Time will tell if service life will be extended. However, in the case of pre's and other input gear, such as phono pre's and CDPs, the more recent models use 6922s and 6H30s. ARC advises that these audio/signal tubes be replaced at 4-5,000 hrs. Certainly in the case of ARC gear, I am not aware of any tube, at least in current models, that has a 10,000 service life. Perhaps, longer tube life might be found in gear from other companies.

I think the question at hand is whether there are suggestions or recommendations out there in audio-land that can help extend, or at least not shorten, tube life -- whatever the factory's recommendations might be. I think you put at least 2 recomendations out there in your post. Thank you. Your advice makes a lot of sense.

Two things. ARC wants to maximize the listening pleasure of it's owners, without much regard to the cost of tubes.
So they want to be certain the tubes in use are always going to be excellent, and never 'wearing out'.
Thus thier recommended replacement intervals.
No problem in my mind with thier philosophy.

Another thing is the preamp tube, and the power tube are really two very different animals as far as tube life.
Power tubes are run hard, and wear out pretty fast, and when they fail, it can be fireworks. So you want to replace power tubes when recommended.
Preamp tubes (depending on the usage and design) can last a very long time. And never do any explosive things. (well possibly, but i never heard of it) A few designs do run preamp tubes hard, some notorious preamp designs went through 6DJ8 tubes fast! So preamp tubes (and preamp type tubes in an amp) can be used until they start getting bad/noisy.
You do NOT want to leave a power tube running without a person present. the exploding/fire etc possible distructive death of a power tube is real. And so its the fire hazard.
Not so for a preamp tube.

I leave my VAC Standard preamp on 24/7 with a pair of 12ax7 and a pair of 12au7 in there, and a sealed case, (separate SS power supply) with little generated heat, I expect them to last pretty long even on 24/7 (as i listen over ten hours a day average anyway)
And finally playing music or idling. Preamps are mostly class A 100% so the tube is run at 100% at idle, and actually less when playing music.
Power tubes can be anywhere in the class "A" to class "AB' spctrum, and depends on how they are biased etc.

Cd player tubes are in there as a preamp tube or tube buffer. and are not stressed much. They should last a long time also. ditto most headphone tubes.
A few BIG headphone amplifiers use real amp tubes though.

Great responses, and all very helpful!

Much appreciated.

Thanks all,

--dan

One comment on ARCs recommended replacement intervals. My cynical side says that it's likely that there is also an element of profit maximization as well as client satisfaction. ARC-sourced tubes sell at a premium and I imagine that they also do a pretty good business re-biasing some of their power amps. If you run a search, you will find that the tube replacement/re-biasing process on some of their amps is pretty complex and not for the faint of heart. Just sayin'; not trying to pick a fight.

"05-11-11: Swampwalker
One comment on ARCs recommended replacement intervals. My cynical side says that it's likely that there is also an element of profit maximization as well as client satisfaction."

Agreed. When I read Elizabeth's post I thought it should have read "Three things", this being the 3rd.
File this revenue stream under 'consumables.'