This analog tachometer was found in Radio Electronics from the 90s. The components used can still be found with some ease.
We found this circuit in an 80's Radio Shack publication. The circuit uses a company buzzer, but...
This is a well-known RC oscillator configuration using a 741 operational amplifier. The circuit is from...
This simple neon lamp power indicator circuit was found in the January 1971 Radio Electronics...