Metal locator (CB7506E)

This simple metal detector was found in a 1960 Sylvania transistor manual. The phone must be high impedance or crystal.

Full wave rectifier filter (CB7582E)
This circuit was found in a Popular Electronics from the 90s. The power source must be symmetrical...
Diac Test Circuit (CB26106E)
We found this test circuit in the November 1999 issue of Electronics Now magazine. The circuit is to be...
Manual Siren (CB13165E)
In the circuit of the figure, when pressing S1 the sound varies according to the value of R2 and...