Found in a 1924 book by Gernsback, this circuit uses a double variable capacitor, a component not very common at the time. Listening was done on a loudspeaker at the time.
By pressing and releasing PB1, only one LED is lit, drawing a number from 1 to 6, as in a die. The...
We found this circuit in the National Semiconductor Linear Applications Handbook of 1994. The...
The transformer inf this circuit is a 6 or 9 V unit and diodes 1N4002. The filter capacitor is 2...