>
>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...
I have heard that story too, just check the water level now and then
to assure you don´t run the amplifier dry.
Good engineering practice? probably not but the plate will not reach higher
temperatures than 100C :-)
You will probably have to live with steamy windows in the hamschack ...
73´s de Johan SM3UZS
>
>--
>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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