[jbothma]

This reminds me of when I built an amplifier around 2002.

Just before this I built a crystal radio - basically a very long wire, a diode, and a crystal earphone. No amplifier.needed because the earphone is so sensitive.

As I got the amplifier all soldered up, I heard radio on a speaker without any signal connected if I touched a metal tool on some contact.

I asked about this on an electronics mailing list and if I recall correctly people were mostly annoyed that I was talking rubbish. But I'm pretty sure something was acting as the diode, I was the antenna, and the amplifier put the signal out.

[molticrystal]

Well one type of foxhole radios had oxidated razorblades touching graphite from a pencil as the detector, I imagine the class of objects that might be too difficult work with practically unpowered expand greatly when you have powered amplification available, and perhaps your tool had a coating or something that acted in a similar way.

[trasz]

Can be done even without an amplifier: https://mythbusters.fandom.com/wiki/Tooth_Fillings_Radio_Myt...

[jfk13]

Perhaps some contact involved was acting as a "cat's whisker" detector. https://en.wikipedia.org/wiki/Crystal_detector

[buescher]

You probably got your amplifier into regeneration. As they say, amplifiers oscillate and oscillators don't. No rectifier needed.