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
It makes no difference. Just bias them all the same!
I go with the transconductance value if I can. Plate current works too but IME is less accurate.

You'll have to bias the tubes up anyway, but if they all show the same transconductance values the bias setting will be nearly the same on all of them. But the thing is, what the tube is doing at half and full power is important too. That is why I go with transconductance.

Thanks.  Well, after yogiboy's post I just slammed 'em in there and biased.


Atmosphere, maybe after a listen, tomorrow I'll re-arrange them.


So for each 4 tubes per amp, I just select the transconductance with the closest value number, correct?
Mercy, they aren't matched that well prof. That's for darn sure. If  within 15% is matched.. You're ok..  You want to match the first number and the second number is what is left in the tank.. pretty simple..

You want those to be in pairs to.. I'd have to see how CJ wired the power valve side, but v1,v2 and v3,v4. CLOSE.. the 46.8 is NOT matched... The numbers don't lie.. No matter how you arrange them the ONE will be over 10%.  It should be 5% MAX... That's if you like matched valves.. 10% is what Golden Lyon call matched.. 5% was the GE (Tung Sol) way..

YES they make a difference in SQ.. Either at the beginning of the valves life or the end, BUT not all of the valves life.. That is why we MATCH even with auto bias.. Just SLOPPY not to... Where we don't lose SQ we lose a LOT of time between valve changes because of ONE valve taking a dump..

Especially for the cost of NOS Matched.. LOL One set is good, though.

Looks like numbers from a Maxi Maker.. I own one.. Great testers..

Regards
Hi oldhvymec.   (And others...thank you!)



Yeah, I was wary of that one number being extra high.  That comes from a replacement tube.   I'd bought two matched quads, but one tube turned out to be bad, and I guess that's the best replacement the proprietor could find.


Another thing:  I'm surprised at the nature of the change in sound this brought to my amp. 



Up until how I'd stuck with whatever CJ recommended at the time, which 6 years ago where the modern Tungsol 6550s.   So that's what I'd used until recently.  I started hearing creeping grain/distortion in my system and figured it was likely tubes.   I've had the CJ Premier 12s since the late 90's and never replaced the small input tubes either!   So I figured it was time just in case.  The original were GE tubes, one 5751
two 6FQ7 per amp.


I ordered the Svetlana Winged C 6550 NOS tubes, and wanted to try tube rolling for the input tubes.   Bought these:


5751 super low noise:


http://www.tubeaudiostore.com/57suplownois.html


And these Mazda 6CG7 / 6FQ7:


https://upscaleaudio.com/products/mazda-6cg7-6fq7


My research on the Svetlana Winged C 6550 NOS tubes suggested they had a rep as a linear-sounding tube, tight bass etc, not overly tubey.Which I was kind of going for.


The results have been, first off, a total lack of distortion and grain, so that problem was fixed.  Utterly gorgeous, smooth, velvet texture and tone.


BUT...an increase in the "tubey-quality" - the bass is less defined, bigger, a bit woolier, less air on top, a teeny bit thinner upper midrange.  And most of all a mellowing of dynamics, punch and density.  In effect it now sounds more like a slightly underpowered tube amp - gorgeous in tone, but lacking some drive and aliveness.   That part is a bummer.


So I'm wondering if it's the 6550s or the input tubes changing this character.    I've heard input tubes can change an amp even more than the bigger output tubes.


Thoughts?  (Anyone?)





I would think a curve tracer would be better for matching tubes, but I'm just guessing.


Well.   My amp just blew.

Sudden loud sound, distortion then silence.   Slight burning smell from amp.   Same amp as the one tube that went bad that I had replaced.


That didn't last long.

Sigh...
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.

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?
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.
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...
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...
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.
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?





 
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.

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.