[Amps] Force cooled heatsink aerodynamics

[Alan Ibbetson]

> From: Bill Turner <dezrat1242 at wildblue.net>
>> I'm planning on using one of these in my solid sate PA project
>>
>> http://www.farnell.com/datasheets/17645.pdf
>
> REPLY:
>
> That is interesting. Do you know what the prices are and where to order
> from?

I am paying just over £100 each, say $160, including the fan. Farnell 
and Newark have a tie-up so I expect Newark can supply in the US.

> Also, I'm curious how your design places a high RF voltage on the
> heatsink. Do you mind explaining?

I am planning on using TO-220 high voltage switching FETs which are 
primarily targeted at SMPS use. The drain is connected to the mounting 
tab. I did look into using a more conventional style of heatsink with an 
Alumina plate as a thermally conductive but electrically insulating 
interface between a copper heat spreader and the main heatsink, but the 
US supplier let me down on delivery and in any case was wildly expensive 
for overseas customers. This approach allows me to bolt the FETs 
directly to two heatsinks (in a push-pull circuit) and float the whole 
assemblies at drain voltage. I don't see this as being much different 
from applying an external anode valve.

At the danger of stating the obvious, I do plan on enclosing everything 
inside a case for safety!

73, Alan G3XAQ