"Sal M. Onella" wrote in message
...

"Jimmie D" wrote in message
news:Ujwsh.298$ch1.65@bigfe9...
I was cleaning up today and came across an old dummy load I had that
looks
like it is made from 2 watt resistors. ITs mounted on a quart size paint
can lid and looks to be a 50 watts worth of resistors. This looks like
it
may have been a commercially built unit and I was wondering what the
power
handling capability would be if the resistors were submerged in mineral

Related, sort of:

When I was in Navy ET School in the 1960's, we had a shipboard radio
transmitter lab which used banks of incandescent lamps for the dummy
loads.
By the time we got to that phase of the school we understood the concept
of
matching to 50 ohms and I wondered then (and now) what the actual
impedance
of a bank of light bulbs would be. (Of course it changed with the amount
of
power applied, since it lit the lamps more or less brightly.)

Nobody ever explained it. It's a wonder we didn't make more smoke than
light. [AN/SRT-14, AN/SRT-15, for those who've been there & done that.]

Also, for excellent heat dissipation and no conduction, a liquid called
FC-75 is used as a heat transfer medium. They literally immerse the gear
in
a tank of the stuff and run it though a liquid-to-liquid heat exchanger.
It's totally inert. We used it in our high power pulse transmitters in
ECM
gear and it's apparently still around [
http://news.thomasnet.com/fullstory/473395 ] . No, I don't have any :-(



Yeah, I am familar with the stuff, its an inert flurocarbon. FAA did some
experiments to see if it could be use in RADAR tx oil tanks to replace PCB
type oil. I understand it worked pretty good, having better heat transfer
qualities than the oil they finally used.


After I got my ham ticket I built a little TX with a 6146 and used a light
bulb dummy load. To get an idea of how much power I was putting out I
measure the rsistance of a photo resistor with the tx keyed then applied a
variable ac voltage to the lamp and adjusted it until the resistor measured
the same and calculated power from the voltage and current measurements. I
wonder how accurate this was.