This circuit was found in February 1976, Radio Electronics magazine. The circuit is quite sophisticated using a fast-acting (thermometric) sensor and analog indicator.
This circuit is from a publication from the 50's. Inductive components are critical, and...
This simple two-transistor circuit used transistors from the 60s, having been found in a...
This circuit uses an oscillator that generates a signal of approximately 1450 kHz to test...