[Amps] New 2 PA design
kg7hf at comcast.net
Sat Oct 16 15:20:24 PDT 2010
You are right, heat and control are the primary issues to solve, and they can be solved in a solid state design just as they are in a tube design.
When the QEX article came out, I contacted JA1DJW about reproducing his article. He was very kind and sent me many emails with details, pictures and some of the critical parts for the amp. I think there are two fundamental reasons the 2.5k isn't rated for full power output in continuous mode.
The first reason is the power supply isn't rated for continuous duty and is maybe a bit under sized for the application. A secondary reason would be the heat issue. Nobuik sent me a heat spreader but I opted not to use it since the heat spreader is about 3.5" x 3.5" x 3/8" copper. I opted to use a 12 " x 8" x 1/2" heat spreader with "copper fins" attached and replicated his machine work layout onto it. Efficiency is more along the order of 60% at the worst, usually better though.
From: Dan Levin <dan at andlev.com>
Subject: Re: [Amps] New 2 PA design
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.
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