[Amps] 3CX800 stray C to chassis?

[Steve Thompson]

Some years ago I measured some valves, including 3CX800. I don't 
think I have kept the results but the general result was that the 
C was about twice the data sheet value, and wasn't changed by the 
mechanical setup unless the metalwork was really close - much 
closer than you would want when looking at a layout.

Steve

> As I do not (yet) own a decent LCR meter does anyone have a decent ball park figure for the stray C to chassis for a 3CX800A7? The side walls are 1.25 inches away from the tube and the lid is 2.5 inches above.
> 
> 
> Also thanks for all the help with my previous questions. I should mention that this is a retrofit to an existing 2m amp and C1 is 6pF maximum and I would like to use this part if at all possible.
> 
> 
> I have a design that works on paper for strays C of 4pF with a Q of 8 using an L-Pi-L configuration as recommended by a few of you. The 4pF stray value does not seem unreasonable but it is a guess. I am sure that someone must have measured this.
> 
> 
> Regards
> 
> Conrad PA5Y