Digital recorder ISD1016 (CB7963E)

Found in a Popular Electronics from the 90s, this digital recording circuit uses an unusual integrated circuit today.

10 kHz PLL Filter (CB15972E)
This circuit has a low level at its output (pin 8) when the input signal has a frequency of 10...
Capacitor Test (CB26188E)
Found in a 1993 Electronics Experimenter Handbook, this circuit uses a multimeter to measure...
Adjustable Voltage Reference (CB1282E)
The circuit is from an old American publication. We can mount it with the BC548 and TIP31. The...