[Amps] Grounded Screen 4CX1500B

David Kirkby david.kirkby at onetel.net
Tue Nov 8 06:59:29 EST 2005

Conrad_G0RUZ wrote:
> For the uninitiated the weasel or whistle or various other names was the
> nickname for the push pull 2 x 4CX250B amplifier published by W1SL which got
> a reputation for not working too well. This was because UK amateurs insisted
> on using the wrong type of surplus socket.


I am copying this to amps, as you appeared to have intended it going there.

If I recall correctly the W1SL amp was published by a ham who later got 
the call sign W1SL, but at the time it was published he was not W1SL. 
But it worked fine for me.

I used a pair of Eimac SK-600 sockets in the W1SL 2 x 4CX250B amp, which 
I bought new from the company that used to be run by John G4FRX (the 
believe) Sorry, I forget name. Tubes were bought new too. Anyway, that 
amp worked very well. It worked pretty much exactly as the Eimac data 
sheet said, producing 600W in AB1 before the grid currents meters would 
move. Anode voltage was 2 kV, screen 300V and whatever the grids 
voltages needed to be (-63V ??) to get the 100mA/tube.

The twin 4CX1000A amp was similar from an RF perspective, but different 
on the DC side, as the screens were grounded. The right sockets were 
expensive, so I made them.

Rather annoyingly I designed the amp and built the sockets, but G8WYI 
payed for its construction and built the rest of it to my design. Hence 
I was not too happy when it did not work!!

I essentially combined (in an unsuccessful way), the RF side of the W1SL 
design, with the DC side of an single 4CX1000A amp published in one of 
the ARRL manuals.

The 4CX1000A tubes were believed to be new as they looked unused and 
were boxed. Later we bought some pulls with no change in performance.

> I don't see any reason why David's amplifier wouldn't work, I bet if he went
> back to it now he'd get it working in no time.

Perhaps, who knows. I know we spent quite a bit of time on it. Not too 
much attention was paid to decompling the cathode, as the caps used were 
not qood quality RF ones. *Perhaps* that was the issue.

> Conrad G0RUZ 

David Kirkby,

Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/

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