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In Reply to: RE: Allen, posted by Neff on October 03, 2010 at 21:20:40
That like 394,000 hours! My KT88s are only rated for 1500-2000 hours.
That really makes me wonder about hours. I always assumed it was hours of being on, but some of these responses lead me to believe that it is hours of being played.
So is the 1500-2000 hours when playing near the maximum rated output?
Lower volumes= 3000-5000 hours?
No signal at all= 45 years?
"Idiocracy" had it all wrong. We'll be there way sooner then 500 years!
Follow Ups:
If the gear goes on and stays on, they are not relevant.
The military had this policy when tubes were king, my father said when new gear came in, it was plugged in and LEFT on, and they had minimal/no tube problems. I once had a US military info sheet that gave tube life of regular tubes at over 100,000 hours under these conditions.
Wish I still had it to show you doubting Thomas's.
Lightning strikes are something else for sure.
Regards, Allen
Allen,
Having many military tube euipment manuals and having scrapped military tube equipment you first have to realize that unless under combat situation tubes were considered an infinite resource and the cost of recalibrating a radar set under combat conditions was far, far greater than the cost of a set of tubes so, yeah, let 'em burn. But the military also published books of "preferred circuits" - I have several from the Navy from the 1960s - that were "preferred" for, among other things, running tubes extremely conservatively far below consumer applications. Also in many pieces of mil spec gear under the cover would be a complete spare set of tubes already broken but really never used (I've never figured out to best describe these as NOS or UOS - but since I've not had the boxes I've settled for UOS prices usually).
So there'a a basic philosophical difference here: first that you don't want to be "caught with your pants down" (we actually detected the planes approaching Pearl Harbor but being unfamiliar with the crude part time radar we ignored them)and; secondly - like much of the military "price is no object."
And none of this addresses the "sleeping sickness" problem identified in the late 1940s-1950s when tube computers came around. Since their power supplies were regulated and very steady - as is our current power line voltages (in general) cut off tubes went dead (preWWII daily 100-115 line voltage swings were common especially in urban areas with much use and rural areas with miles of swaying power lines).
What might help is if you can get a souce of the literature of the day such as back issues of "Radio and Television Engineering News" and several other such engineering publications. I was luckly to puchase a retiring Ham's collection in the early 1990s which cast a different light on tube use during the 1940s-60s. The whole issue of whether to turn off or not was mainly determined by the criticality of the application and the difficulty of replacing the tube that might burn out.
Rob
I refuse to add some stupid bit of trivia here - OOOPS!
...and I really agree with the statement that the military ran their tubes nowhere near the maximum ratings.
Always been a design policy of mine.
Regards, Allen
Also good to note that the cathode poisoning occurred in gear which had long down times in terms of the tube actually being used. That is usually not the case with audio gear. Also note that WE got its reputation from the telephone repeater amps they made which were never turned off.
Stu
"So is the 1500-2000 hours when playing near the maximum rated output?
Lower volumes= 3000-5000 hours?"
If it's Class A, it won't matter but Class A/B does draw more average plate current when driven hard and that would wear out the tube faster.
With Class A operation the average plate current does not change much between no volume, low volume and max volume.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Its hours of being on. That said, when I'm going to be listening to my system on and off during the day, I just leave it on. Not only does this ensure that its warmed up when I'm ready to listen, but the constant heating/cooling from frequent on/off cycling is hard on the tubes too. Just buy new tubes periodically, that's the price of having tubed gear.
Jack
I would think of it if I lived somewhere else. Took two lightning strikes in three years. Microwave, phones, wireless internet etc gone. Cable was fixed for free. Computers & stereo gear was unplugged!
Second strike blew old BX cable out on the whole second floor.The basement & first floor had new romex wiring thus survived. I had to rewire the second floor. Of course, performed the rewiring myself thru out the summer, but should have subcontracted the work!
I'm sure a lot of people (self included) don't like to leave hot amps on when they're not around for fear of fire hazard.
25 years ago my girlfriend was forced to leave her apartment one night after a fire in the one above it caused evacuation of her building. So later that night, after all the trauma over the fire above her apartment, she came to mine to spend the night.
It was in the wee hours of that particular night that my Dynaco PAS 2, left on most of the time, chose to erupt into flames...
I'm still around, just not listening at the moment. I don't leave my amp on if I'm leaving the house, but If I'm around doing chores and know I'll listen on and off during the day, I leave it on.
Jack
Would using a 10A variac help tube life? Or decrease it?
I am new to this but have been using it as I've seen light dimmers really increase light bulbs life to many years. That way inrush current can't kill the filament on turnon. I suppose those ICL's sold would help too. I also stop under 115V to help on old amps not designed for 122V. Heaters are running higher at todays voltages too.
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