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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
jjss49's avatar
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jjss49
6,608 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...
atmasphere's avatar
atmasphere
11,574 posts
 
The burning smell is likely either a cathode or screen resistor.

I suspect this may not be the amp's fault- the tube itself might have simply arced. They are most likely to do that right after shipping. It does not matter that the tube is brand-new- it was likely shipped untested from the factory.


Generally speaking when buying brand new power tubes, if you make it past about two weeks of normal operation they'll be OK. I would send the tube back and get a replacement since they do have a 90 day warranty.
prof OP
3,435 posts
 
Thanks for the input fellas!


The idea of shipping the Premier 12 kills me.  First, I'm not sure I even have a shipping box and these are super heavy.  It would be damned expensive and likely a long time before I got them back.


I'm taking them in to the local shop again to see what they have to say, as the other places I tried were busy.


If it needs more particular care I believe there are some specialty tube amp techs within my city area who, I hope, can do a pretty thorough look over.

atmosphere:  I bought these:

https://www.dougstubes.com/power-tubes/6550-kt88-kt90/svet-winged-c-6550.html

As I understand it, that's a reliable place for tubes and he measured each before they went out to match.   Does that not indicate working tubes to begin with?





atmasphere's avatar
atmasphere
11,574 posts
 
 
Does that not indicate working tubes to begin with?
Of course! But that is very different from saying that they won't arc right after shipping. Its like I said- if you make it two weeks after installation and you don't have a failure you'll probably be alright.
prof OP
3,435 posts
 

Thanks atmosphere.
I'm rolling the dice one more time taking it in to the local shop.  If things fail again I'll have to escalate my efforts.
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