[Amps] [Moon-net] 4CX250B in P-P 2m?

[Ian White GM3SEK]

Dr. David Kirkby wrote:
>SM6CKU wrote:
>> Hello guys
>> Anyone knowing about a 2m kW amplifier in push-pull with 2x4CX250B?
>> A friend of mine is asking....
>> 73 de Ben
>> _______________________________________________
>> Moon-Net posting and subscription instructions are at 
>>http://www.nlsa.com/nets/moon-net-help.html
>>
>>
>
>Yes, I know it would be *seriously* over-run. The maximum anode voltage 
>is 2 kV
>and the maximum anode current per tube is 250 mW. So a pair of tubes 
>should take
>no more than 1 kW of input power.
>
In old American magazine articles, "kilowatt" always did mean input. 
Maybe that is the source of the misunderstanding.

A kilowatt output can just about be done: increase the B+ to 2.5kV 
(on-load), use a big blower, forget any pretence about linearity, bias 
the tubes into class B or C to give them a rest on key-up, then use lots 
of drive to turn the tubes on again... and pray a lot.

In the years when 4CX250Bs were the only VHF/UHF tubes available, I did 
this for moonbounce on 432MHz... even made a special control board to 
keep the tubes alive  :-)

These days, with tubes like the GS35b and the even bigger tetrodes so 
freely available, it is hardly worth using 4CX250Bs at all.



-- 
73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek