[Amps] MOSFET biasing

[Danny Pease]

Anyone have any experience with biasing MOSFET's for linear service,
specifically the MRF174? 

I have a 144 MHz 600 watt amp that uses 3 boards of pairs in push-pull.
The existing bias arrangement switches between a negative cut off
voltage and a positive voltage high enough to cause the transistors to
draw some idle current.  All transistors see the same bias voltage.
Since the transistors area not matched to each other in any way, the
bias is fixed at a level that causes the lowest transistor idle current
to be about 300 mA .  Some other transistors may run as high as 1 amp of
idle current. The power source is 28 VDC.

Am I correct in assuming that I would be better of with a circuit that
would allow me to set the bias on each individual transistor or should
the bias voltage be the same for each push-pull pair?

What amount of idle current is needed to provide linear service with the
MRF174?

Danny NG9R



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