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QUESTION about Installing "Matched" Tubes

Hey folks,

I have Conrad Johnson Premier 12 monoblock tube amps, 140W/side. And I’m replacing the old 6550 output tubes.It’s 4 6550 tubes per monoblock.


I usually just replace the tubes with whatever CJ recommends a the time. But this time I splurged for Svetlana Winged C NOS tubes. I bought two pairs of matched quads.


My question is: How do I go about placing them in the amps? Is it required, or best, to put each matched quad in each amp? Or does it matter which monoblock all the tubes go in?


I’m asking because at the moment I’m not sure which tubes are actually matched. They were measured before shipping, with the Plate Current and Transconductance number’s written on each tube. But frankly, not being an electronics guy, I don’t really know what they mean and how it helps me match the tubes, if they do.


So for instance, there are numbers on each tube:



46.8/4740
42.2/4410

41.4/4870
38.8/3970

42.8/4830
39.5/4470
41.3/4810

41.9/4770

Do I, for instance, try to find the 4 tubes in which the Plate Current numbers are closest in value? Or the Transconductance number?


NOTE: My CJ amp allows for user biasing of each 6550 output tube!


Thanks for any info!
prof
jtcf's avatar
jtcf
1,589 posts
 
You might want to get the amp checked out. A bad cap maybe?Time to get them both serviced if that's the case:-/
IME the small tubes "flavor" the sound, the power tubes have the most effect on the drive and bass punch.
prof OP
3,435 posts
 

Yeah, I'm going to have to take the amp in to the local shop now.
BTW, the sudden loud ripping distortion then silence, amp no longer on, burning smell....does that sound like a fuse?
Would a tube dying suddenly cause that and if so would the tube look obviously burnt or anything?
jjss49's avatar
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jjss49
6,605 posts
 
prof

sorry to hear your cj blew -- if there is a burning smell then no, the fuse did not do its job of protecting the amp and the internal components

hope jeff and the guys at c-j take care of you soon!  i am curious to know what power tubes they are recommending these days... very good kt88's out of russia under tung-sol and gold lion labels these days, excellent sound, very good reliability and q.c.
acefactory
59 posts
 
I'm with jjss49 on this. Very sorry to hear of your experience, and it does indeed sound like the amp blew one or more components. Although a local shop can no doubt get it back up and running fairly swiftly, the techs at c-j can sort out the tube issues and (hopefully) bring both monoblocks back to original specs. This road of course is a bit more costly and time-consuming, but delivers a much better (and reliable) overall outcome...
jjss49's avatar
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jjss49
6,605 posts
 
especially with pieces as nice as prem12 monos, having had something go up in smoke, i would heartily lean towards having jeff and his techs make sure the amp is a-ok and working fully to spec... they are now 20 y o amps so worth a top to bottom check of all components... as we know, heat degrades, the these babies run hot in regular operation - they can probably make sure the input tubes are well biased and quiet

hope you send em back prof... they deserve the trip to virginia to get proper care from the maker...
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