The operational amplifier for this tone control found in a 1977 Signetics manual may be the 741. The power supply must be symmetrical and the signal cables short. The bass gain is 20 dB.
This simple transistor tester circuit was found in the February 1968 issue of Radio Electronics magazine....
This powerful inverter provides a high-quality sine wave signal. I found it in a Radio Electronics issue...
This squelch is activated by its own noise, acting automatically. It is used in communications...