[UK-CONTEST] 70 MHz 4CX250B Linear

[Ken Eastty]

Hi Andy,

 From memory mine uses a passive grid arrangement. I have about 20W 
available from the H/Brew Xvter which is sufficient to produce 160W O/P 
however I'm not very happy with the Pi O/P circuit as the efficiency 
seems much lower & runs hotter than my single 4CX250B 2m linear which 
uses a tuned line and works very well. Apparently some people use 2 x 
4CX250's on 4m, maybe mine isn't so inefficient after all.
Perhaps one of these days I'll try a tuned line on 4m but it will have 
to be folded it it's to go in the original case.

73...

Ken

G3LVP



>
> Hi
>
> I know a lot of folks use a single 4cx250 on 70mhz in NFD etc.   Does anyone here have any design notes, particularly on the input and output circuits.  Despite having two successful homebrew amps for 6 and 2, I'm having difficulty getting this right for 4M, particularly the input circuit.   I'm interested in LC details and what RFCs you're using.
>
> I've tried the input circuit from http://www.qsl.net/g3uvr/4cx250/4cx250.htm  but can't seem to get it to match at all.
>
> I'm sure I'll get there if I mess around long enough, but I'm a bit stretched time wise at the moment.   As an alternative, if anyone had a working 4M amp they no longer had a use for and wanted to sell, I might be interested!
>
> 73
> Andy
> gm8oeg
>