I wondered if any of you clever people would be able to explain some stuff regarding the mosfets to me.
I am aware that the mosfets are operating as source followers and that one biases them to be above their ohmic range. (With the heaters as one of the biasing resitors)
If I understand correctly that would mean that the mosfets would be permanantly fully on, with all the power flowing from drain to source and therefore into the heaters. Now most of us are running 12 or 17v circuits for the tubes and it's pretty clear to anybody that 12 =! 48. Does that mean that the heaters (which are more or less lightbulb filaments as far as I'm aware) are purely current dependant? Do they just need their 12V*0.15A=1.8W? or does the mosfet only provide them with the appropriate power/voltage? If so how does this work? (I've been unable to find much information on this subject despite a fair amount of googling, it's always too simple or too hard for me to understand.)
Another part of my question is once again related to the source follower nautre of the fets. We apply plate voltage + amplified music ac to the fet gate (high impedance therefore low current) and we get a low impedance, high current output from the source. The question is probably the same as the last, how come we just have a fully open transistor but instead get a buffered version of the original?
If somebody could explain this topology or could point me to some decent reference material on the subject I'd be very grateful,