This circuit is from American documentation from the 70s. This configuration appears in this section obtained from other sources. The signal is sinusoidal determined in amplitude by D1 and D2.
Using a piezoelectric sensor of the time, this circuit was found in the February 1994 issue of...
We found this circuit for old tape recorders in the December 1972 Radio Electronics magazine. The...
This constant current circuit was found in the October 1993 Electronics Now magazine. The current can...