Re: The James Knights Co. oscillator, 4.0 kc
Yes, it's indeed homebrew and it uses components that span some decades. By the way, I've never met a 7805 in that case (see pics).
I reversed the circuit around the transistor and it looks like an oscillator where the big tube is the resonator element, so Jon is right. Looking through the top hole with a strong light I see a small trimcap. Let's see if I can open the can without damages.
Paolo
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