NEUTRALIZATION

[W9BHI]

Hello all,
I am running a pair of 4-400's grid driven as a class C plate modulated RF deck.
I am using a pi input tuning network to match the grids to 50 ohms and it works quite well with a good match.
I am using a Flex 3000 for a driver running about 10 watts of drive to get the required 24Ma of drive.
This deck is running on 20 thru 160 meters.
20 meters is very unstable and the grid drive is all over the map when the plate tuning control is adjusted due to the fact there is no neutralization involved, just swamping on the grids.
Is there a neutralization scheme that works with a pi input circuit?
Thanks,
Don W9BHI

[w4bfs]

sounds like its oscillating .... ballast the B+ to prevent runaway ....sniff with a neon bulb on an insulated stick (very carefully of course) .... if it glows purple rather than orange then its likely a vhf parasite ....find out where its most active in the circuit and this is where stoppers will be most effective ....

if not a parasitic then what did you use for a swamping resistor and what value ?

[W7TFO]

Tetrodes seldom need neutralization.

As mentioned, I vote for parasitics.

73DG