This current meter with many scales was found in a 80s American documentation. The operational amplifier is from that time, uncommon nowadays.
The circuit in the figure trips with a negative transition of the input signal, its output...
The basic frequency of this circuit is determined by the capacitor of 470 nF and the adjustment of the...
The load current can be adjusted up to about 1 A. The transistor can be TIP32 or TIP42. The...