We found this circuit with JFETs in a Radio Electronics magazine from June 1969. The circuit has its assembly described in a complete article. Equivalent transistors can be used.
We found this source with the CI 723, common at the time, in a 1989 paper. Power transistors must be...
This old voice circuit suitable for telephones of the time was found in a Radio Electronics from...
We found this frequency meter circuit in a 1974 documentation. The circuit is powered by 12 V and...