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In Reply to: RE: Do tubes get "tired"? posted by airtime on April 14, 2015 at 06:28:00
Regarding small signal tubes...
I'm of two minds. Manufacturers like Audio Research tell you that tubes like the 6922 are good for only about 5000 hours. Turn off the component when not in use. With a new preamp in the main system, I adhere to their recommendation.
Just for grins, I've experimented with doing the opposite. For years, I ran a Manley tube DAC that used 12AU7s 24x7 and couldn't tell any difference even when I changed them once a year just because after nearly 9000 hours. I replaced that unit with an ARC SP9 MKIII and similarly have left it on 24x7 since last summer using 7308 tubes. I'm gonna run them until I can tell a difference or they die! I have four spare 7308s to use afterwards, but I'm finding that continuous use is not necessarily such a bad thing - again with small signal tubes.
Follow Ups:
Hey, Stat:
Does the SP9 utilize a stand-by mode, or are they fully energized all the time? Just like ARC reccos, CAT says to turn off my SL1 when not in use and it removes power completely when shut down. I had a Counterpoint preamp that always kept the filaments warm and had to be unplugged from the wall to completely shut it down. Mike Elliott the designer of that pre felt that the thermal cycles of going from stone cold to hot was more damaging to tubes than leaving the filaments energized. My Acoustat servos keep the filaments warm all the time too, but from what I understand Jim Strickland did that mainly because the humidity in Florida necessitated keeping the amps warm to drive off the moisture. So, I've had amps/preamps that keep things on and I've had them that keep things off, and I can't say I've really seen any differences in how long tubes last. Would be interested to hear what you think after you've finished your testing.
The SP9 offers a mute circuit, but I'm pretty sure that only disconnects the output. I think it remains fully energized. While not tubes, I also keep the Stasis 3 on at all times.
I used the Acoutat X with servo amps in the late 70s. I remember the relay that would click and wake up the amp for full operation.
The 7308s in the preamp were installed 9/12 although I wasn't running them 24/7 before I moved the preamp to the garage. Indeed, they are longer lasting versions of the 6922 with an expected life of around 10,000 hours. I see no reason why I can't easily double that.
Yeah, it was a neat idea to have the servos wake up and go to full power when they detect signal on the input, but it didn't do much for the sound of the amps. All that wake up circuitry has been removed from mine. The filaments stay warm all the time, and then there's a toggle switch that brings filament voltage fully up and kicks the relay to turn on all the high-voltage stuff when you want to listen.
I thought both the 7308 and the 6922 were 10,000 hour rated tubes. The differences, if I remember correctly, were that the sections in the 7308 were guaranteed matched to with 10% from the factory, and they can take more voltage on the plates than the 6922. Either way, that's a looong time to run a tube.
I was lucky enough to have scooped up a mint Sencore MU150 several years ago, and after I've had a tube in service for over a year usually, I'll pull it and run gain test on it while hitting the "life-test". Any tube that shows significant drop in reading gets the hook. On that basis, most tubes seem to have a serviceable life for me in the 2-3 year range. Keep us posted how the test comes out.
I thought both the 7308 and the 6922 were 10,000 hour rated tubes. The differences, if I remember correctly, were that the sections in the 7308 were guaranteed matched to with 10% from the factory, and they can take more voltage on the plates than the 6922.
You're right. I must have been thinking about the difference between the original 6DJ8 and the 6922. Having said that, ARC used to recommend changing after 5000 hrs on their old web site.
I'm curious. Because I have a fully rebuilt Sherwood with original tubes circa 1958. The preamp tubes are RCA blackplates, outputs Phillips 7189's. And the driver tubes are of course the pain in the @ss 7199.
I don't want to start rolling tubes. Being my farting around days are over. I'm in listening mode now. But I do have a full set I bought from Jim McShane.
charles
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