Neutralization capacitor connection point: question

[AB2EZ]

I was looking at the schematic of my KW-1, and also the schematic of a Johnson Valiant... and I noticed that the neutralization cap connects directly to the plate terminals of the rf output tubes.

When I looked at the schematic of a Johnson 500, the neutralization cap as connected to the tank side of the plate blocking capacitor (which seems like a better design from the standpoint of the peak voltage across the neutralization cap).

Is there a subtle reason why the designers of the KW-1 and the Johnson Valiant would have chosen to use the approach they used?

Stu

[k4kyv]

The Gates BC1-T puts the neut capacitor on the tank side.  The reason I can see for running it directly to the plate is the possibility of rf phase shift through the blocking capacitor.  This would more likely be a problem on the lower frequency bands where capacitive reactance would be the highest.  The Valiant and KW-1 both cover 160, but the Johnson 500 is one of those "all-band, 80-10m" rigs common in the 50s.

My homebrew rigs each use two neut caps and each one  goes directly to the plate of one tube in the push-pull circuit, since I don't use a blocking cap; the +HV is series fed to the plate through the tank coil.  I believe the unmodified T-368 uses series feed and no blocking cap, so the neutralising cap would go directly to the plate.

[KM1H]

Phase shift is indeed an issue and Im rather surprised the Johnson 500 did it that way. It would be interesting to put one on a SA and see how much the cancellation holds across the bands.
It works well for a BCB TX thats set and forget but it tends to be a problem in multiband rigs to find the sweet spot. Of course the lower cost just "may" have been a factor.

Carl