Tube Amp question:TUBE replacements: explain MATCHED?

 @moose89 -

            Lots of pics and info, available from this page:

https://www.google.com/search?q=cary+slm+100+for+sale&oq=cary+slm-100

                                       a review:

https://www.stereophile.com/tubepoweramps/cary_audio_design_slm-100_monoblock_power_amplifier/index.html

What are SLM’s?

@immatthewj -

     I've looked for/at the smallest ammeters and (thus far): haven't found anything I could mount anywhere on my SLMs' chassis, for the convenience of not reaching for my Fluke.

     Hanging a couple on the amp stands and hard-wiring to the Bias jacks, would be a possibility, but: I'm SO lazy.

     Besides, it seems: with a good quad of output tubes in each monoblock, their relative biases seldom change.     Only: slight bias variations, consistent/the same in both, according to what's coming from the wall.

     The SLMs were my step, following the Rocket 88, which didn't have the juice to satisfy my SPL Jones (inefficient speakers, at the time).     No need to look further, as the SLMs' excellent transformers and circuit design made adequate power and the realism/presentation I sought, an easy reach, with judiciously chosen parts.   

     They were treated early on, to better RCAs, 5-ways and IXYS HEXFREDs.   Since: every cap has been upgraded (ie: Duelund cast-PIOs for coupling, ClarityCap ESAs in the B+, etc ).

     Of course: the optimum, NOS 6SN7 search was another enjoyable, illuminating and fun-filled journey.

                        Yeah: I'm FULLY invested in the SLMs, with NO regrets!

                                                     Happy listening!

@rodman99999 

I was thinking that if Moose didn't have a multi-meter he could have killed two birds with one stone (always good to have a multi-meter handy) and if he did have a MM, he could have saved the $ on that one and just bought the leads.

But that's okay.  And if you've seen the pictures of the CAD 1205 MKII, that has bias meters built into the front face plate so one can be monitoring the bias all the time, and I can see where that would be nice.  I guess one could do the same thing with that fancy Cary meter?

You had a couple of SLM 100s?  How did you like them?  I once tried out a Mesa Barron and that got me wanting mono blocks and seriously considering the 100s.  I remember talking to Kirk Owens about them, & he sounded unusually (for him) animated.  I wound up buying a couple of secondhand ARC VTM 120s from a guy who was selling them via a listing in the back of Stereophile; those amps sure sounded good, but I used to cross my fingers & grit my teeth whenever I turned them on, so for the sake of reliability I bought my V12 in '01.

Oh well, ramble on. . . .

     The nicest thing about buying that meter from Cary: it includes the same 3' test leads (with attached 1/4" plug), that came with my SLM100s.   

              Or: was it the Rocket 88 (Oldtimer's Disease strikes again)?     

                                                        Anyway:

     Would have been simple/easy to make my own, but I'm SO damned lazy: it was greatly appreciated! 

                    Then again: that IS a stiff price, for a mA dedicated meter.

@moose89 

just my two cents, but I’d work on getting the EL84s & the 12AX7s real good first (before or even IF you decide to try to find a way to go hog wild on the outputs).

Sounds like you have everything you need to check & adjust your bias, so good for you on that. The only thing that I would have done differently on that is to have bought a versatile multi-meter versus that fancy meter that Cary sells. But you can keep that in mind for next time in case the one from Cary ever breaks.

It is always a good idea to put matched power tubes in your amp or integrated. Do this even if it isnt required. You have a much better chance of similar longevity if you start out with matched tubes. Best to buy power tubes that have been burned in for 25 to 50 hours when possible. This is no guarantee that there tubes will age similarly but it doesnt hurt. Further there is no reason not to buy this way and no good seller will charge significantly more for matched tubes.

     I WISH there were yet honest-to-goodness, NOS KT88/6550 valves out there, that could be described as, "reasonable".

     The supplies of Sylvania, GE, Genelex and Tung-Sol output valves, have long been dwindling and the prices (if they can be found): breathtaking.

     Even the authentic (before the St Petersburg plant was destroyed) SED =C= tubes are way up in price, IF/WHEN available (not often).    Funny (to older-than-dirt me, anyway), that tubes made as late as 2012, should be considered, "NOS", BUT: they did come close to the presentation of the afore-mentioned champs.

Y’all are great! Yes, I ordered the plug-ins and accompanying meter from Caryaudio.com  $120.

and I’m hoping there are some reasonable NOS quads for output. I’ll wait til we get past our newest tragedy distraction in our political world, and like toilet paper, supply and demand will settle $  down. 

@moose89 -

     The information that blackdoghifi gave you, regarding YOUR Cary amp’s output tubes and why THEY should be a matched set, is absolutely correct.

      Given that all 4 of your valves share one bias voltage; not having a matched set MAY result in crossover/notch distortion, which is never good.

                                   Also: immathewj’s instructions = +1

I just looked at the bias instructions for the 808 and the bias is adjusted by the same procedure as the two Cary amps that I own. A plug (with a + lead and a - lead) insert into a receptacle in the back of the amp; you will need a multimeter that will read DC milliamps. Connect the leads from the bias plug to the leads on the multimeter (the Cary bias plug leads have alligator clips on them) and after the amp is warmed up, you can adjust the bias pot. I always back my bias pot all the way down and start from scratch when installing new output tubes or lugging the amp in at an unfamiliar environment.

@wspohn

That’s what I told the individual who was helping me troubleshoot my Cary when he told me about how he had to bias his ARC. I said, "That’s interesting." But, I also said that I thought that it must make for a better tuned amp. I once had a pair of ARC VTM120s, & I vaguely remember hooking up leads for the multimeter to legs of resistors on the circuit board, and then adjusting the bias pot (on the board) with one of those plastic screw drivers you referred to. That typed,  on those ARCs that I owned each bank of four 6550s were adjusted together.

As far as checking bias, I bought a dozen new reissued Tungsols going on a year or so ago, and I have actually been checking mine after every several hours of play time. Mainly what I am watching for is to see that the small changes in bias that occur are happening on both sides simultaneously (which for now, they are).

@immatthewj 

Interesting that they do bias in banks - my CJ does each one separately but it is simple - use a plastic screwdriver to adjust each of four lights until they go on, then just until they go off again  Takes a couple of minutes to do all four tubes and CJ suggest that you do this every 6 months as maintenance.

@wspohn 

I remember an email exchange with someone on another audio forum who was helping me troubleshoot one of my amps.  Biasing was part of the subject matter, and I remember him telling me about the ARC that he had (I cannot remember which one) that he had to bias each tube individually, including the input tubes.  He said that it was a time consuming endeavor.  On my Cary V12, I have a bias pot for the 6 output tubes on one side and a bias pot for the 6 on the other side.  My Cary SLA70 just biases all 4 outputs together. 

Nice that there is bias adjustment. Best case is individual bias adjustment (my CJ amp has this) which means that you don't need a set of matched tubes.

however I need the plug-in to check the Bias, and I guess a meter?

I just looked at the bias instructions for the 808 and the bias is adjusted by the same procedure as the two Cary amps that I own. A plug (with a + lead and a - lead) insert into a receptacle in the back of the amp; you will need a multimeter that will read DC milliamps. Connect the leads from the bias plug to the leads on the multimeter (the Cary bias plug leads have alligator clips on them) and after the amp is warmed up, you can adjust the bias pot. I always back my bias pot all the way down and start from scratch when installing new output tubes or plugging the amp in at an unfamiliar environment.

In the case of your amp, all four KT88's are biased at the same time. If they are not matched for current draw, you may have one or two drawing more current than the others. While the total may be correct,  the individual tubes will be running at different levels. Depending on how far out they are, it could be audible.

The EL84's don't need to be matched, and for equal gain, the 6922's should be matched. That said, I've never seen preamp tubes so far out to make much of a difference unless one was defective.

groups of 4 with very similar responses.   Nice to have but not required.

The Rocket 88 requires (per manual) electrically and brand matched tubes. Some amps require this and some amps don't. 

Your amp uses 4 kt88s.   You should install 4 of the same brand.  You can buy 4 more of any brand you want.  

Matching refers to tubes within the set of 4.  Since tubes have inherent variability in their responses, people test a large lot and pick out groups of 2 or groups of 4 with very similar responses.   Nice to have but not required.

Now isn't a great time to buy tubes.  But it is good to have a spare.  Your KT88s probably have a log expected life so it isn't urgent to get a spare set.  I would buy a single tube of the same brand you have installed to use as an emergency spare and wait for prices to go down.

Jerry