[Milsurplus] [ARC5] Hello Smart People: Output Network "L"

[Ian Wilson]

I've seen similarly puzzling effects with an 813 in a pi network
using an inductor with switched taps. The thing would dip weakly and
not produce expected output. Changing to another tap close by would
make more change than I would expect.

I have tried taking all the power away and putting a resistor to ground
in place of the tube, then looking into the pi network with an antenna
analyzer. These results also indicated that something was not right.
Replacing the RF choke made a noticeable difference, and at the time
I thought there was a resonance.

On reflection, however, I suspect that what is happening here is that
there is a grounding problem and/or a stray capacitive or inductive path.
Changing the pi network coil slightly changes the phase shift around the
network and this in turn combines with the stray to produce odd effects.

This sort of effect would be cancelled out by neutralization although
unless it's a pure capacitance that would only be effective over a small
frequency range.

This is still a theory, but since the observed effects can't arise from a
simple pi network, there have to be other L/C in the circuit somewhere.

73, ian K3IMW