On Oct 18, 10:04*am, (Scott Dorsey) wrote:
I once built a push-pull class C amplifier using 833 tubes, with three
continuously tuned inductors that could handle 80M through 20M.

Kewl. Neutralization in push-pull is in my experience much more
tractable because you just tap off the signal from each phase, feed it
through the neutralization cap which is nominally identical to the
plate-grid capacitance, and into the grid of the opposing tube.
Mathematically the plate-grid capacitance is constant as you change
bands so to zeroth order neutralization may not have to be adjusted
for band changes. Did the same neutralization setting work across the
bands?

I once tried to imagine a scheme where all 4 inductor taps in a push-
pull front-panel-bandswitching scheme were switched with ceramic
switch wafers actually inside each of the coils, and all the wafers
are ganged with plastic cog belts. In the end I went with a much
simpler plug-in coilset scheme.

Sure, but can you get them free out of someone's trash? *All the big
planar grid tubes I found being thrown out are destroyed...

It just occurred to me why ham amps with driven grids are so hard to
neutralize compared to diathermy machines that donate their old tubes
to the projects: You don't need to neutralize a diathermy machine at
all!

Tim N3QE