TUBE BIAS, socket to me!

Elliott, check the paperwork that came with your Cayin and see if it states that it has "automatic biasing" or something to that effect. If not, there should be a procedure on how to do it. Are there any test points on the top or back of the chassis?
If it must be adjusted and the measurements are internal flip the amp on it's back and use the spring loaded hook type test leads with the power off. Make sure there is a load (speakers) on the outputs unless stated otherwise. You want nothing connected on the inputs. They should have a setting (usually in millivolts) that you adjust a pot to. That will set the current flowing through the tube. Some amps have an individual pot for each tube and some share a pot between both tubes in a push pull type amp. If I recall, yours is a push pull design.
I suspect that it's auto biasing or more than likely you would have red plated a tube if your swapping tubes. Uneven current matching on the tubes can lead to a runaway current situation that results in red plating.
Don't rely on your tube tester to match tubes, they don't test the current at full operating voltages.
There is a Fisher forum on AK, lots of information over there on adjusting those amps.

BillWojo

Elliott, it may still be autobias unless you found out otherwise. A tube amp that has autobias has no test points or meters, like my MC40 monoblocks. But, just because it has none of those doesn’t mean it has autobias. Most older tube amps didn’t have that stuff, required you to get in there and measure. No chance you have a schematic?
Can you contact the company and get some info?................................................                                             On Edit: I searched and found biasing instructions and emailed them to Elliott. It is not autobiasing.

BillWojo

@oldhvymec, the old Hickok testers and the like tested MUTUAL CONDUCTANCE at low voltages, not at the operating voltages that they were likely to see. Makes a huge difference.
Would you pressure test a gas cylinder that routinely is filled with hydrogen at 2000 lbs by checking it with only 500lbs of pressure? Of course not, wouldn't even dream of it.
So why would you test a vacuum tube that runs at 450 VDC plate voltage with 100VDC or less. Sure, it can tell you that the tube is conducting but not how well it will conduct under a real load. That's best left to either testing in the actual amplifier or a modern tube tester like a Amplitrex AT1000 that can put up to 500VDC and 160 milliamps on the plates. There is another modern tube tester that sells in kit form that can test to much higher voltages as well. Both of these testers tie into a laptop computer and can plot curves for the tube under test. THAT's the kind of tester that can match tubes, not the older ones. Neither is cheap, I'd love to have one myself.
Not saying that the older tube testers are worthless by any means, they can be used for testing shorts (very important), gassy tubes and microphonics along with a doing life checks and basic health. But to match up tubes? NOT. That is best done either with one of the advanced testers or in the amplifier itself and a test meter. Anyone telling you different is either ignorant or trying to get over you. The best tube sellers today are using the latest test gear, the old TV7 type tube testers were the shitt years ago but old tech today. Times have changed my friend and this new tube testing technology is awesome.

BillWojo

Elliott, if it has those tiny little pots they make adjusting tools for that. I always called them "tweakers" LOL, Radio Shack sold a set of 3 for just a couple of bucks, made of plastic.
If your going to do this, just make sure that the power is off when you attach your insulated clip leads. Use your meter set to DCV and check the PS caps to see how long it takes them to bleed down. Most PS have a bleeder resistor across the caps that will discharge the high voltage in just a few minutes.
Not a bad idea making an insulated tool, easy to slip and make sparks/do damage.
I bet Greenwood has the proper tools, do I really need to give YOU an excuse to go over there? LOL.
BillWojo