This circuit was found in a 90’s Popular Electronics. The circuit is used to analyze noise in vehicles. The output must be in a low impedance headset.
This half-wave regenerative control was found in an old RCA manual. The circuit can be designed...
I found this circuit in a documentation about thyristors from the 70s. The circuit uses a diac...
Up to some minutes intervals can be obtained from this circuit. The circuit can use a lamp (or...