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 simple circuit controls the brightness of an LED from LDRs, NTCs, PTCs or other resistive sensors....
This common configuration of voltmeter with differential pair of FETs was obtained in the 1994...
We found this digital timer circuit in a 1994 publication. The power is supplied by 12 V, which is the...