[Amps] Grounded Screen 4CX1500B

[David Kirkby]

Shawn Tayler wrote:
> I have done just the opposite direct for this test, injecting the signal
> on the output and watching the level in the input. 

If the tube is off (as it was when this was done), and there are no 
magnetic devices like isolators, I don't see what difference it would 
make. The system would be a reciprocal two-port so you should get the 
same result in either direction.

To do it while the tube is on would be another matter. Perhaps we should 
have made a cheap sensitive RF source and detector for this - putting a 
spectrum analyser on the input and a tracking generator on the output 
when the amp was on would have been brave to say the least!

> I would adjust the

> input and output tunning for maximum coupling then the neutralization
> adjustment for minimum, watch to keep the loss > 10dB better than the
> expected stage gain.

We did adjust tuning & loading to get the maximum coupling, and 
neutrilisation for minimum. This was checked with a spectrum analyser, 
so it was not checked at only one frequency, but swept.

It's a long long time ago I last looked at this, but I don't think the 
neutrilation was really necessary. The isolation was so much more than 
the stage gain.

-- 
David Kirkby,
G8WRB

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