Tube Amp question:TUBE replacements: explain MATCHED?

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.

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.

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.