We found this frequency meter circuit in a 1974 documentation. The circuit is powered by 12 V and has 8 digits. Changes can be made using a prescaler to reach higher frequencies.
A touch in this circuit turns-on the lamp or the relay. Power supply is according the lamp or...
This an old commercial receiver found in a year 1958 magazine. The circuit uses some transformer...
We found this very simple cable fitting circuit in an Electronics Now from the 90s. ...