This simple tester was found in a Popular Electronics from the 90s. The circuit is powered by two 9 V batteries since it requires a symmetrical source.
This 1965 Philips circuit uses old company transistors like the BFY51 and BFY50. The circuit is...
This circuit with an operational amplifier was found in the magazine Radio Electronics of...
This trigger produces an output pulse when zeroing the input signal. The circuit is from a...