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 circuit uses a small photocell to trigger an auxiliary flash. The circuit is from a 1991 PE...
This circuit is from a Popular Electronics from July 1990. The magazine no longer exists, but the...
This telephone circuit was found on a 90's EDN. It keeps a flashing LED to indicate that there was a...