On 10/15/2010 8:43 PM, Dan Levin wrote:
> The big issue with parts like the ARF-1500 is managing the heat. For
> high duty cycle use, like contesting or RTTY (or worse yet, contest
> RTTY :-) ), you are dealing with dissipating something like 1500 watts
> of heat (assuming 50% efficiency running class AB) being generated in
> an area about one inch by three inches.
>
> That is a solvable problem, but not for most ham's who don't have a
> background in thermal engineering. Notice that the HL-2.5KFX is not
> rated for full power high duty cycle use - in fact it shuts down when
> the heatsink reaches 100 degrees C.
>
> It is much easier to deal with the heat if it is being produced by
> lower power parts, spread over a larger physical area. NB: For the
> ragchewer or DX'er this is much less of an issue, because the lower
> duty cycle makes life much easier than for contesters.
The problem comes with the delta T through the heat sink compound, the
silicon chip, and the transistor body. I think the lowest thermal
compound (Highest thermal conductivity) is still arctic silver although
Masscool looks pretty good. There is little that can be done for the
transistor itself except to lower the outside temp.
73
Roger (K8RI)
> Also, although people are constantly talking about transformerless
> power supplies for these higher voltage parts, in the real world the
> best source of power supplies for high power solid state amps is the
> telecom surplus market. 48 volt switching supplies rated at 50 amps
> are frequently available on eBay (e.g.) for under $100 - and they are
> small and light weight.
>
> ***dan, K6IF
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