look at (and copy) the final circuit from a BE-5A (broadcast electronics) FM
transmitter.It's very simple and very stable too. It likes about 200 watts
of drive from a IPA. Will run nicely with 5000 volts at about 1 amp on the
plate. In the BE transmitter the tube sits in a cavity, with the plate being
slide tuned. A coupling loop sits close to the tube....Eddie

"Onno de Vries." wrote in message
om...
My name is Onno de Vries and i'm living in the Netherland and building
big amps is my hobby.
I just bought a 4CX 5000A on a radio market here for a good price (180
Euro) including socket.
Becourse the price was so good i took the challenge to build a 88-108
Mhz final from it.
After some experimenting i found out that the anode resonator a a bit
of a problem course of the high cappacity of the tube.
I try to do it with a double output coil (together Almost a half wave)
wich you see in manny designs for 144 Mhz amateur amps using for
example the russian tube GU84.
This works but it has a terrible efficiency,about 25%.
I hope that somebody can give me some Info about making a good and
high efficiend tank with this kind of tube.


Greetings.....Onno