This is what I like the most about Elecraft. You have persons like Wayne,
Ron, Tom, and Don coming out and freely giving this technical information.
One would never see Yaesu or Kenwood or Icom doing this. Thanks Guys for the
knowledge and the helpfulness.
john-n3drk
----- Original Message -----
From: "Ron D'Eau Claire" <[EMAIL PROTECTED]>
To: "'Elecraft e-mail reflector'" <Elecraft@mailman.qth.net>
Sent: Sunday, February 12, 2006 12:36 PM
Subject: RE: [Elecraft] K2 Contest
Evert wrote:
2) Can this amplifier be tuned for 1 hour on a dummy with full output
at any band without any semi-irreversible side effects?
----------------------------------
If you mean at the rated output for 100% duty cycles modes, 40 watts out,
the answer is Yes. But I'd not try it at 100 watts. The 100 watt spec
assumes you are running SSB or CW that has a much, much lower duty cycle, so
the average power output remains 40 watts or less.
Several years ago I helped test the VCO stabilization mod and needed to
temperature-cycle the K2 as in normal heavy use. I did that be transmitting
into a dummy load for periods of 1/2 hour to 1 hour, occasionally longer. I
ran the K2 at 100 watts and keyed it in CW, using a repeating CW memory to
keep it running. The internal air temperature between the KPA100 and main K2
PCB got up over 50C (120F). The KPA100 heat sink was too hot to hold my hand
on it. Since the intent was to simulate very heavy use of the rig in a real
situation, I did not provide any ancillary cooling. I did that dozens of
times. No problems were encountered.
I did not run those tests on various bands, so I can't speak to any
significant temperature differences. But there are some slight differences
in efficiency. Does your KPA100 make a full 100 watts output on all bands?
If not, there might be a problem with your output filter on one or more
bands that is reducing the efficiency more than it should. That would
produce excess heat as well. If you are getting full rated output, I'd
expect that any differences noted are normal.
Be sure to tighten your final PA transistor mounting screws after several
hours of operation as described in the manual. That ensures you maintain the
intimate mechanical contact needed for efficient heat transfer. It only
needs to be done once. I think my screws took about 1/2 turn after the rig
was run in for several hours, then they remained "snug".
As others have pointed out, there is exit cooling cleverly hidden between
the fins on the KPA100 heat sink at the forward end. So if you use the heat
sink to keep your coffee cup warm, don't spill any!
Ron AC7AC
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