This transistorized stage has a high gain, being adjusted by VR1. The circuit can be used as an excellent audio preamp. We found this circuit in a 1996 English publication.
This 1967 Raytheon circuit uses an optical coupler of the era and has a range of 800 to 200 Hz....
This interesting digital counter with relays with complementary outputs was found in the Radio...
This circuit uses a diode as a radiation sensor. The operational ones are old because the...