This blocking oscillator configuration was found in a 1964 American book. The circuit can be designed with modern transistors and the frequency depends on the transformer.
Found in a 1966 documentation, this “coin finder” uses components from the era operating at 2.1...
This circuit is from a documentation on the MC1539 from Motorola and may, however, be implemented...
The 747 is an old operational amplifier, but the configuration applies to modern operatives. In...