On 4/30/2012 10:48 AM, Paul Christensen wrote:
>> In solid state broadcast transmitters, there is always APC (automatic
>> power
>> control).
> It's possible for the ALC mechanism in our amps to manage that much to the
> same degree as commercial automatic power control. Its just a matter of
> applying the right algorithim to the ALC bus. I suspect Elecraft uses an
> ALC algorithm in its 500W amp that's much the same as the one in their K3
> which has excellent transient and long-term power management time constants.
>
>> The Harris MW-1...now there's a transmitter I'd like to forget...
> Not for me. Once it was upgraded to the MW-1A, it was nearly trouble-free
> at WLBK between 1980 and 1983, the year I graduated from NIU.
>
>> The obvious solution here is liquid cooling.
> Yes, but how is that implemented at low cost and low maintenance to the end
> user?
Liquid cooling is no where near as complicated as most make it out to
be. OTOH it is *different* A tube that might require enough air at
full power to be obnoxious could likely be cooled with a gentle flow of
water out of a 1/4" or 3/8" tube. Most tubes with finned anodes are
relatively easy to convert to water cooling as well. You have to use
distilled or DI water. A 5 or 10 gallon tank will hold enough water to
run you for hours at the legal limit. If it's an open container, freeze
some distilled or DI water into bricks and add as needed. You can get
fancy and add refrigeration, but it's not normally needed. Then you have
to have a long enough run of tube to handle the voltage which is usually
done by coiling the tube on a plastic form inside the amp.
To do it with Solid state, you simply make a heat spreader with imbedded
water passages and don't have to worry about long lengths of tubing.
Water cooling is quite simple in computers, even gaming computers that
are well overclocked, but they run nowhere near the dissipation as a
tube or SS amp.
I've since sold them, but I picked up a bunch of undrilled aluminum heat
sinks that were 10 X 12 and 12 X 14 inches for about a buck each.
>> High volume/low velocity only works when you have a suitably large surface
>> area of heatsink. Heatsinks aren't cheap, and, if the goal is to maintain
>> a
>> small form factor, you have design criteria that are mutually exclusive.
The PL172/8295A is an excellent example of low velocity, high volume.
It's only 1KW dissipation, but a muffin fan can cool it. It's not all
that much larger than an 8877, but is very easy to cool. You are't
going to be able to squeeze 2300 to 2400 watts out of it. OTOH it will
run the legal limit with some to spare. I don't know if it has enough
emission for that or not.
73
Roger (K8RI)
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