[Amps] 4CX800 Linear

[Steve Thompson]

On Wednesday 05 November 2003 00:45, Glenn McNeil wrote:
> Hi Gang..
>
> I'm after some advise...as are most on this reflector I suppose.
>
> I'm building up the 4CX800 Linear featured on the Svetlana Website as Tech
> Bulletin Number 42.
>
> Part of the plate tuning requires a 70mm round disk to approach the earthy
> side of the plate line..which is an aluminium sandwhich seperated by a
> teflon sheet. This disk approaches the earthed side of the plate line, near
> the tube. The other end has an adjustable tap to feed the RF to a type N
> connector.
>
> Constructing this cap relies on a good earth where the adjustable shaft
> passes through the RF Anode box to the outside world where it has a knob or
> such to allow tuning the anode.This is easier said then done..around hear,
> anyway.
>
> Is there anything wrong with using a wide spaced variable cap mounted
> inside the anode compartment in the same relative postion, one side
> attached to the anode line and the other neatly earthed by the caps normal
> construction with spring loaded shaft etc. I have a box full of Polar brand
> ceramic body, silver plated variable caps that I have ratted out of various
> junked gear over the years, and this seems a much neater way of doing
> things.
Problems with a variable - possible unwanted resonances, and still a poor 
current path to earth through bearings/bushes etc. Better is to replace the 
disk with an 'L' shaped flapper, screwed solidly to the chassis along the 
short flange, bent so it springs away from the anode line, and tuned by 
pushing it forwards with the disk screw mechanism. I use .01" brass for the 
flapper. Put a PTFE button on the end of the shaft. You can see something 
like it at http://w3ref.cfn.ist.utl.pt/cupido/gu74amp.html

Steve