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There does not seem to be a clear consensus on the internet, but I thought it might be fun to get opinions on tube life and power cycling.
I like to use my KT-88 based tube amp at different times from morning until night, but I don't necessarily listen from morning to night. I have power cycled my amp as many as 3 times in a day and I can't help but wonder if I am doing more harm than good by not just leaving it on.
Another point to consider is the energy usage .vs tube replacement cost. Obviously to more time the amp spends off the better from an energy usage standpoint, but does the saved energy offset the cost of new tubes which may be needed sooner from increased power cycling?
So I guess my main question is: At what point would power cycling be more tube life friendly than just leaving them on? More than 2 hours, 3 hours etc.
"Idiocracy" had it all wrong. We'll be there way sooner then 500 years!
Follow Ups:
have standby mode so I guess I'm very lucky in these regards.
If a thing's worth doing, it's worth doing well
(Proverb)
Some power tubes will have less than 2000 hours of life when operated at maximum ratings. Life increases dramatically when they're operated more conservatively. And some small signal tubes (which are operated at a small fraction of maximum ratings) can last 100,000 hours or more.
Edits: 10/04/10
While I think it's stupid to waste energy just to preserve a tube - I live in one of the most heavily coal strip mined counties in the USA and that's where your power comes from in one way or another - it's true that cycling the filaments on/off does somewhat shorten the life. But..........possibly even more importantly, leaving most tubes powered up without signal can lead to a condition that was referred to a "sleeping sickness" where the cathode lost emission although the filament glowed merilly along. This condition was first noted at a problem when tube analog computers came along after WWII and many of those numbered industrial versions of the 12AX7 and 12AU7, etc., were created to resist sleeping sickness. But, as best I know, these manufacturing changes weren't applied to consumer tubes and I've seen several power output tubes including 6L6GC, 6CA7, and 6550 lose emission just from being left heater with plate voltage and no signal as well as the dual triodes. So even if you insist on trashing more of this planet unnecessarily - and all of us who love the sound of tubes are already compromised - you wind up possibly killing the tubes that you probably paid too much for to begin with.
Rob
I refuse to add some stupid bit of trivia here - OOOPS!
And what do you guys think about using the Speakers/Standby switch? My Scott has a Speakers switch that I use a lot. I have always used it thinking that should preserve the pwer tubes. What do you think? Also, obviously I turn on the amp with the Speakers switch in Off position.
Escobar
Scott 222D
Yamaha YP-D71 TT
Martin Logan Motion 4 Speakers
Hopefully growing!
Is your switch marked "standby" or just "speakers ON/OFF" like on my Scott 350B? If it is the later it's not a "standby" switch instead what it does is kill the speakers so that you can use the headphones without disturbing others by switching the power output from the speaker terminal strip to an internal 20 ohm resistor. While this will reflect a tad more impedance back to the output tubes and you'll probably turn down the signal level so as not to fry your ears (truly dependent on modern listening levels and phone efficiency) but the output tubes will still draw "most" of the current that they would under normal low room listening levels (If I can remember to - terrible memory these days - I'll measure the current flow in this state the next time I rebias my 350B - I set it up with individual cathode current monitoring resistors/7591 and individual bias).
Since the purpose of "standby" isn't to preserve output,or other, tubes but instead to provide an "instant on" environment the way standby is accomplished can kill tubes as easily as not having the standy and simply turning down the amp or having no signal (assuming the theoretical noiseless environment). Those schemes that either removed B+ or lift the cathode from ground do preserve tube life but some circuits do things like short the control grids together on a push-pull output or remove screen grid voltage or, in at least one amp, short the PI control grid to ground. In all of these cases the amp may be subject to "sleeping sickness" and output tubes with very few hours on them simply lose emission. The control grid shorting scheme I've noted in particular is more likeley to cause this but still the best way is to turn the dang thing off - the "off" part of the cycle isnt' doing any damage - and install some sort of ramp-up "soft start" turn on that doesn't thermally shock the heaters/filaments and in this day and time there are tens if not hundreds of ways to accomplish this. And if one is an obsessive purist concerning devices in the line side it would be easy to have a ramp up device that is switched totally out of circuit using a "make-before-break" switch once the tubes are hot.
Rob
I refuse to add some stupid bit of trivia here - OOOPS!
Yes! It is a Speakers On Off switch.. so in the end.. It doesnt help a lot to use this switch..
I have read about a method of biasing in where you need to put a resistor in the output in order to check the bias. Should using the speakers switch be similar? Most probably not, but it could be true considering most of the people I have seen talking about biasing their Scott amps have 222Bīs and Cīs. What do you think?
Best regards,
Escobar
Scott 222D
Yamaha YP-D71 TT
Martin Logan Motion 4 Speakers
Hopefully growing!
... to a similar question.
I say leave the amp on and only turn it off as little as you can.
My two tube preamps are on 24/7/365.
My two tube poweramps go on two hours before I have a demo or want to listen for myself. They do go off when we close the joint.
Tubes will last LONGER if you don't turn them on & off all the time, and the gear will sound better when fully warmed up.
Regards, Allen
I can state this. I know of a tube scanner that has been left on since 1965 and still receives signals with the original tubes.
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!
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.
The filament will last much longer if only used as needed. A great example is I tested a NOS 01A tube manufactured in the 1920s. Tests same as new!
Is that a fact ?
I quite doubt it, Western Electric 300b's have been known to run 24/7/365 for several decades on end !
Regular light bulbs most often fail at turn on, not whilst running under normal conditions.
The only vacuum tube I've had which actually failed on me was an exotic military Bendix 6900, it's filament opened on turn on...
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