This circuit with RIAA equalization is from 1985 US documentation. The circuit has a flat response of 150 Hz to 40 kHz. The power supply must be symmetrical.
With S1 closed, when dark, the triac will supply the load with the power set in R4. The LDR is...
This interesting circuit with a neon lamp and a transistor was found in Radio Electronics magazine...
This crystal oscillator is indicated for the calibration of IF steps of common radio receivers. The...