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

[jeff millar]

The use of copper in heat sinks is primarily to spread the head from the 
transistors to the metal better, since you transistors run cool, the 
problem is more in the heat sink to air interface.  Fans will help 
enormously.  Try putting one or two muffin fans blowing directly on the 
fins, actually mount the fans on the heat sink.  After that it's more 
heat sink area.

jeff, wa1hco

Dan Sawyer wrote:

> 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
>
>
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