[morzh]

I asked because I never heard a cap used for a transformer radios.
With AA5 (and in the article you showed it is AA5 with the curtain burner cord) it is straightforward.
WIth the transformer it is not. Starting from the fact that when it is plugged in it could oscillate, and second unlike in AA5 where it is usedc in a circuit with stable active load, the tranformer radio becomes the load with everything taht is the load, and it is not really stable. So the dropout across the cap might vary.

And there was another thread with a curtain burner cord, so I thought you meant to popst there maybe.