[Amps] cooling a high power rf mosfet amp??

[Dan Sawyer]

All,

The MRF154 amp is working well. The gain is 19db in the 80 and 40 meter 
bands. The move from 30 Volts Vcc to 50 Volts was uneventful. That move 
went without incident and it resulted in improved gain. However, it 
results in increased heat. Right now there only a 500 watt supply 
connected and the heat sink rises to "hot to the touch" in 3 minutes. 
The actual devices are only slightly warm to the touch. Most of the heat 
appears to be transfered to the sink.

1. I assume most of rise is due to bias current?

The heat sink is a 5 x 8 x 1/2 inch thick plate with 1 inch fins. They 
appear to be steel of some kind. The heat transfer across the plate 
seems very uniform.

2. How much more or less efficient would a 1/8 inch copper plate be??

3. How much more efficient would a cooling fan across the fins be??

Thanks in advance,
Dan