On Sun, 28 May 2006 19:41:21 GMT, "JC" wrote:


"Roger" wrote in message
.. .
On Sun, 28 May 2006 13:47:35 GMT, "JC" wrote:

Ahhhh... That is just a pice of Silastic (TM) sheet wide enough and
long enough to form a chimney when wrapped around the tube. I can't
imagine it'd take much engineering. It's a very crude, but effective
design and easy to make if you have the material.



Roger,

I proposed a single rectangular piece to wrap like they do on their 8874
amps. I even gave them dimensions, and a good picture of my 8874 mounted in
the amp. A round continuous piece would also work. So far two business days
have elapsed without a reply from Alpha. I hope to hear from them on
Tuesday. I'll keep you posted.

For my brief tests I used a 10" long X 2" wide X .02" strip of Mylar
wrapped around the tube. It worked fairly well, but got de-formed from the
heat. I later jumpered the fan resistor to speed up the cooling fan. For
some reason the MLA-2500 fan speed relay was not kicking in the high speed

I'm trying to remember how the fan was set up in the 2500. I think
you are going to need to pressurize the chassis to get enough air flow
through the fins of the 8874s and they do take more air with a higher
pressure drop than the originals. Those little suckers are expensive
too.

Good Luck,

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

mode when keying the amp. I need to look further into that wiring, and see
what is going on there. There is a button to enable the high speed fan
option, but it does nothing until the thermal Klixon OT-switch clicks on,
and then the fan goes to hi speed.

Jim