We found this circuit in the 1957 Raytheon transistor application manual. The transistor can be a BC558 and the common 6 V relay, just by using this voltage in the supply.
We found this interesting configuration in a 1976 technical documentation. Equivalent diodes can...
This circuit can generate signals of different frequencies, switched by a DC voltage. The...
This circuit, from a publication from the 1970s, can be implemented with more modern transistors and 6 or...