----- Original Message -----
From: "Ian White GM3SEK" <gm3sek@ifwtech.co.uk>
To: <amps@contesting.com>
Sent: Friday, May 20, 2011 8:07 AM
Subject: Re: [Amps] GS-35b heat sink
> Paul Whatton wrote:
>>I remember a conversation with Ian GM3SEK about heatsinks when I was
>>building my GI7b & GS31 2m amplifiers (apologies if I misquote you Ian,
>>you'll probably pop up and say something). I also suggested heat sink
>>compound but Ian pointed out that the tube-heatsink interface
>>temperature was too high.
>>
>
> That may not be true of modern high-performance heat sink compounds...
> but the second point below is the more important one:
>
>>He did suggest that the machining on the tube anode & heatsink were not
>>great and that it might be a good idea to stick them in a lathe and
>>skim them to improve heat transfer. I didn't actually do this but it
>>seems a good idea to me.
>>
> The poor surface finish of the GS35/GS31/GI7 metalwork is sure to be the
> greatest barrier against efficient heat transfer between the tube and
> its anode cooler. As we know from high-power RF transistors, the aim is
> to make the contacting surfaces so smooth that they *almost* don't need
> heatsink paste at all. Then apply the paste as thinly as possible (a CPU
> cooler is a very good example of how *little* heat sink paste is
> actually needed).
>
> The sand-cast anode coolers on the GS31 and GI7 can't be very efficient
> either, because of the small number of fins. One option might be to
> replace these with US-style coolers salvaged from dead 8877s and
> 3CX800s. It should be possible to shrink fit a solid copper plug inside
> of the cooler, with a fixing hole through the centre and a turned flange
> to mate onto the Russian tube. (Just an idea; I haven't tried it.)
Ive done that using glass base 4X150 coolers on 8072's as they were just
soldered in place and removed with a propane torch. I havent been successful
in removing 8122 coolers and I do have several dead 8930, 3CX800, and
7213's. How do you remove those coolers?
Another thing Ive tried is using an Eimac 3-500Z anode on a 8072, it works
well at 300W with a small muffin fan and could probably be pushed a bit
harder.
Carl
KM1H
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