Frame aerial Crystal set.

[Pat Pending]

... The picture? Why a radio, of course!

Did this picture feature a genuine speaker fabric insert, by any chance?

If you think you'd like to try using one of those peizos yourself, bear in mind that they can benefit from a series resistor or choke as they have a very high capacitance. He got the idea from a guy who posts designs for passive sets on the net.

73. Andy

Hi Andy.
Piezo sounders used in crystal sets need a "parallel" resistor, reason is the DC component from the detector has no path, it eventually will charge up the sounder and volume will decay to almost nothing.
The value actually varies it can be anything from 2meg to as low as 10k, it all depends on the sounder.

Hi Trevor, I meant as well as a parallel resistor, as some of the big sounders can have 50 or so nf of capacitance that can load your tuned circuit heavily......that station log you've got there is better than you would get on many a commercial radio..respect. Andy