We found this circuit in an English publication from 1969. It shows how we can implement a bridge null detector using common general purpose transistors.
The frequency of this circuit depends on C1 and, for the indicated values, it is 1 kHz. Equivalent...
This configuration with the LM383 appears elsewhere on this site. The circuit shown was obtained...
This circuit was obtained from HAM Radio magazine in an 80's issue. The FETs are types of the time...