Jack Schmidling wrote:
Dave wrote:


What type of circuit: grounded grid or ground cathode?


It's class C with the filament grounded through a meter.

Leakage with the tube removed indicates inductive coupling between the
input circuit [grid] and the plate tank circuit.


I just tried it without the tube and it seems to have nothing to do with
the tube. When both input and output are resonant, 5 watts in gives me
5 watts out.

The input is a toroid under the chassis so it is not likely inductive
coupling. What I just found was that it goes away when I disconnect the
NC at the plate end.

What on earth does this mean?

I suspect the NC is NOT providing feedback of proper amplitude AND phase. A
connection from the plate to the grid is inadequate. The feedback MUST connect
into the grid tuned circuit.

Another reply speaks to this issue.