Peter Frenning, OZ1PIF wrote:
>Ian et al.
>
>I'm running a single GI7bt (the ruggedized version) on 144MHz with 400W+ out
>on SSB and running extensively WSJT (30s on 30s off 100% output) with 300W
>out, using only an 18W muffin for cooling!
>
>No change to the anode cooler, and using the "flowerpot" trick for
>concentrating the airflow.
>
>See my homepage for details....
>
>From: "Ian White, G3SEK" <G3SEK@ifwtech.com>
>> 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.
>>
I was thinking about what's needed for low seal temperatures and long
life. Peter's experience only shows that his tube survives... but these
Russian tubes have very wide production variations. If the thermal
contact between the cooler and the anode was as poor as the one that
Traian describes, then it might need a lot more air. Fortunately the
tubes are cheap and extremely rugged, so if it breaks you try another
one.
BTW, I remember some folklore that the Russian hams used to use GI7Bs
with vapour cooling. They had an open-topped pot of water screwed to the
anode, and a chimney in the top of the cabinet for the steam to escape.
They had to remember to pour in more water before it boiled dry... but
very carefully...
--
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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