"mark" wrote in message
...
So, for someone still trying to grasp this topic (thanks to the OP) as
well,
what are the tangible effects if the tubes do not match?

In a self-biased class A amplifier, there will be a DC current in the OPT,
leading to earlier and unbalanced low frequency distortion, basically,
reducing the max. power output below say 100Hz (or 10Hz for a Turner OPT
:P ). As I said before, Gm differences have little effect when both tubes
are always on.

In a class AB amplifier, where one tube turns off during part of the cycle,
it's important that they be matched for Gm because that tube is all alone,
the other isn't there to cover its 'mistake' so to speak. Most class AB
amps are adjustably fixed biased, so differences in grid voltage (to get an
equal bias current and Gm) are inconsequential. However, many commercial
amps used a solidly fixed bias, requiring tubes matched for Gm, Ia and Vg.

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms