[Moon-net] 4CX250's .. Air

Doug McArthur tikaluna at bigpond.com
Sat Nov 8 00:31:37 CET 2008

All good technical advice given here on the reflector but remember air flow.
The best check is to place an ARRL on the top of the air out let.
If it does not lift when you turn the blower on then its not big enough!

Thermal drift is a problem (grid 1) when you run real goo. It is
possible to get 'reliable' 1250 watts in a RIW configuration for 
reasonable tube life periods
using good 250R's.(G3SEK used to get 1500 but he was more daring .. 2.5kV Ip)
An absolute stiff screen supply is essential. (Big bleeds). I never 
went above 2.1kV but Ian ran 2.5kV.
Screen current is the killer and flash over protection with MOV's is 
also absolutely essential.

Beware the 'brand new never been used' 1942 tubes being sold today!

There are now far better options, but the thrill of an always pending explosion
is a fond memory!  (Always during a critical QSO.) I still have boxes 
of dead ones I should
have chucked years ago!  Memories!

73 Doug VK3UM

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