[Al (astral highway)]

That’s a good illustration of a strict condition.

Years ago now, when I first mended (I won’t say ‘restored’) a brown box 60s valve radio, I didn’t know anything about transferred impedances. I figured it would be smart to disconnect the loudspeaker of my set for initial power -up after fixing a motorboating problem.

There was a bright blue glow in the output valve and then I thought, ah, I’ll measure that ovevoltage! So I disconnected the mains, lifted the primary hot side and then had a look. I was stunne that I cold draw an arc from the lifted lead to anode connection. I had a small but effective line output transformer!

Suddenly I understood while the bypass cap was rated 1200V.

I had the sense to stop the experiment pronto, but it was some years before I began to actually understand transformers beyond this naive level and learned about the Thévenin equivalents of a transformer circuit.