Tube Amp question:TUBE replacements: explain MATCHED?

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.

@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. 

@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

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).

@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.