We found this bridge circuit in Electronics Now magazine from September 1995. The instrument can be from 50 uA to 1 mA. The trimpot value depends on this instrument.
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...