Hi Mike, and all!
> I already have a
> large heat sink that is slightly bigger then the cold plate.
I also have a big heat sink, courtesy of XQ2PSP. I intend to first see
how much heat my amp finally produces. Maybe, JUST maybe, I can do with
a big, fanless heat sink. That would be ideal. But it's unlikely. And
before adding a noisy fan, I would rather use water cooling.
> The
> cold plate is aluminum but the copper tubes pressed into it are quite
> close to the other side.
In that case, forget about using it without a heat spreader! But with a
good heat spreader, those aluminium cold plates are excellent. And safer
against leaks than most other designs. Just be sure not to break the
tube ends. They easily go, from fatigue or whatever. We use those things
at work, and have had extensive water damage in our equipment because of
fatigue failures of these pipe ends! But then again, in ham use the duty
cycle is about 1% as much as that for the mentioned equipment... so it
should be quite safe.
> I was thinking to use all three copper heat sink/cold plate/finned
> aluminum heat sink,
Do you mean "heat spreader" when you say copper heat sink? Otherwise
that sandwich makes little sense!
> weight not being much of a concern for me. If the
> water pump failed I would at least have the assurance that there is
> something to bring it back down in temp as long as I let of the
> keyline.
Yes, you can do that... Double stitches are stronger, I guess! ;-)
So, now the news for all interested people in this group:
I spent the last three days sarting a little project: It's a 1:100 scale
version of the MOSFET EER amplifier I have in mind. 15 Watts out, at the
same impedance levels as the big one will have. The idea is using this
little guy as a cheap test bed for the principle.
So far I have the RF part ready, a synchronous-switched push-pull
circuit. I used cheap BUZ30 MOSFETs, just because I had a few in my junk
box. They work surprisingly well. Input is with a center tapped
transformer, output with a common mode choke (50 Ohm drain-to-drain). A
5-pole 0.1dB Chebyshev low pass filter restores the sine wave. At 160
meters, the efficiency is a whopping 89% from DC input to RF output, and
the third harmonic (which is the strongest) is down by 58dB. The
linearity from DC input to RF output voltages is very good too. Now
comes the next step, making an RF amplitude detector and a modulator. I
will make a simple linear one, which has a fast response, so that I can
experiment with various delays introduced at will.
Maybe I finish that part before I have to go working again... Then I can
test the IMD performance of this concept, study phase lag effects, AM to
PM effects, and so on.
Manfred.
--------------------------
Visit my hobby homepage!
http://ludens.cl
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