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.
An interesting application that can be implemented with the LM139 is the pulse width modulator. This is...
This circuit converts a positive voltage to negative, with maximum output current of the order of...
This amplifier is suggested by Sanyo and can excite loads of 4 ohms with a power of 4.5 Wrms. The...