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In Reply to: RE: Interesting question posted by Sondek on April 16, 2015 at 06:33:58
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.
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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.
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