Douglas R Snowden wrote:
>
>Tore Sandström wrote:
>
>> Ask W4EMF (w4emf@bellsouth.net)! He is installing 3 x GI7b in a Drake L4B
>> amp. Hes friend, KV4H Danny, is converting a MLA-2500 to 2 x GI7b. He
>>has already coverted the MLA1200 to one GI7b. Danny has removed the original
>>heatsink and installed fins so he can use a muffin fan from a PC.
>How does the original heatsink come off? Glue? Screws?
>
One big slotted nut, leaving a round flat surface and a threaded post.
The original anode cooler is sand-cast, with a relatively small number
of fins, so it really isn't very effective and transferring the heat out
to the air-stream.
Once upon I time, I thought of replacing it with a much more efficient
anode cooler from a dead Eimac tube (4CX250 or larger) and making an
adaptor piece from solid copper... but I never got around to it.
However, I doubt that a muffin fan would be suitable for cooling any
"external anode" tube unless you use *really* big fins with a minimal
pressure drop. Muffin fans are very good for moving large volumes of air
where there is no flow restriction, but they are not good at forcing air
through the small gaps in a typical finned anode cooler. For that you
need a centrifugal (squirrel-cage) blower.
People who use the GI-7b for 1296MHz generally change to water-cooling,
using a water jacket that slips over the threaded post and makes good
contact with the flat surface.
--
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
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