Cheap headphones for your crystal set 

Dr Peter Crystal! 😂

Could you be more specific about the type of piezo transducer?

Some years ago I built a single FET regenerative radio. This too called for some high impedance headphones. At first I used a crystal earpiece, but a pair of 600-ohm headphones, about 80 years old, which, in the 1950s, my uncle had given to my brother and I, together with a home-made crystal set, also worked pretty well. A supplier on e-bay suggested using an Eagle products LT 700 transformer, together with a modern 32+32-ohm headset, with the earpieces in series, making 64-ohms. This transformer was a driver transformer for a transistor radio push-pull audio output stage, using germanium transistors. They were common in the '50s and '60s, but were no longer needed when silicon transistors became the order of the day. This also worked well, using the centre-tapped secondary as the primary winding and connecting the tip and ring of the stereo plug to the primary. This isn't a very accurate impedance match, but modern magnetic materials produce much stronger magnets than the old 'phones, making modern headsets, even cheap ones like I used, very sensitive. There's also an Eagle Products output transformer, type LT44, which was used to drive a 3 to 8-ohm speaker. This didn't work very well. These two transformers are often supplied as a pair, and , rather surprisingly, are still available.

Hi Peter, where can I get a transducer and what do you actually mean by it?

Wow, amazing!

That is a clever idea.

Hi Peter, That's an unusual way of using a piezo transducer to solve a needed problem. 73 WJ3U

Thanks Peter. Very innovative and very clever...

Thanks Peter! Great tip for the youngsters!