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I have a Cary SLI-80 equipped with KT120 tubes. I just noticed today that one tube is dark, no illumination at all.
I swapped positions and it is still dark.
I turn it on and it plays fine, both channels are there and equally strong.
Shouldn't there be a noticeable difference in volume at least?
I can hear no difference from channel to channel.
What gives?
Thanks for any help you can give me.
Follow Ups:
"I can hear no difference from channel to channel."
This is yet another example demonstrating that you can't believe what anyone tells you about the subjective qualities of stereo equipment. Measurements with test equipment are an absolute prerequisite to all else!
Not criticizing the OP, just pointing this out for the benefit of those with whom I've often disagreed. They themselves have sometimes (accidentally) mentioned that they couldn't hear a difference between two amps with entirely different components. No wonder...
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Buy Chinese. Bury freedom.
Did you try biasing the tube that is dark? If it can't be biased it must be defective.
The bias is set for the pair of tubes and I just checked them, it was almost exactly half of what it should be, on the other pair of tubes the bias is correct.
Bad tube I guess!
Bummer, the tubes probably have less than 1000 hrs on them.
Thanks
It's too bad you lost a tube.
Don't run the amp with just one good tube on that side. It's hard on the output transformer and the other tube might get itself in a "run away" condition.
I have no idea why you can't hear any difference between the two channels.
You should be able to. The channel with only one good tube will have much less power and much higher distortion.
The DC of the one tube is not being counteracted by the DC of the other tube and that leaves the output transformer in saturation.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
This just in!
I was in the process of swapping the tubes out for a set of 6550 that I have when I mixed the bad tube with the good ones by mistake. I put them all back in and thy all light up now and bias perfectly.
I just don't know what to think.
I am going to leave it on to see if it dies again.
No offense taken Triode Kingdom.
I always thought I had a good critical ear but at age 61 maybe I have lost it.
If that is so maybe I should enjoy it as I don't need to sweat the small stuff anymore and just enjoy what I hear after all these years.
There may be less difference than some people think. You have the right idea; if it sounds good to you it is good to you. Don't become a specs freak and forget to enjoy the music.
Edits: 04/14/15
Vinny, I couldn't agree more. Trust your ears and not so much specs!
Jim
ARS VS-110
Customized Bottlehead Foreplay II
Preamp
Magnepan 2.5R's
B&W ASW 300 Subs
Ah Tjoeb Tube CD Player
w/Siemens E288CC's
MaggieMate X/O's from subs to
2.5R's
When you find the bad tube again, resolder the heater pins on the tube (2 and 7 counting from the key way clockwise looking at the bottom of the tube)
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
"I always thought I had a good critical ear but at age 61 maybe I have lost it."
Hell, you're still young, just like me (age 62). It's true the uppermost octave is quickly fading, but frequency response isn't the only thing that makes music sound right. The great majority of the audible information resides in lower registers, and I can still pick out every instrument in an orchestra when properly played back. Many of my younger colleagues at work can't even come close to that. Good luck with the amp, sounds like you have an intermittant tube. Follow Tre's advice and you'll be OK. :)
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Buy Chinese. Bury freedom.
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