This is a simple tubed mixer from the 50's. The circuit does not include the power supply and has 3 inputs with independent controls. The tubes are double and the inputs are high impedance.
This interesting bandpass filter using an operational amplifier 741 has its cutoff frequency...
This oscillator takes advantage of the 2000 ohms headphone inductance as the oscillator circuit coil....
This circuit was found in an English publication from 1967. The circuit is for listening on a...