We found this circuit in an English publication from the 60's. The transistors are of germanium of the time and the headphones must be high impedance magnetic.
An stable multivibrator with 50% of duty cucle can be mounted using the 555 as shown by the...
This circuit was found in the old Mullard transistor reference manual from 1960. The circuit uses...
We found this circuit in a 1976 documentation. The transistor and the integrated circuit must have...