This circuit from a Popular Electronics from the 90's can generate signals from 0.03 Hz to 3 kHz depending on the value of the capacitor and resistor.
This circuit can also be used as a shield if the excitation is made with 5 V and the output stage...
This is a Japanese commercial radio from the 60s. The superheterodyne circuit of 7 transistors for medium...
The maximum power of the controlled load depends on the triac used. The circuit is from a Radio...