The purpose of this circuit is only to increase the input resistance of a multimeter, since there is no voltage gain. The batteries are 9 V and operational equivalents can be used.
The integrated circuit can be any operational and T1 can be a BC548 and T2 a TIP41 in this circuit of a...
We can make an oscillating relay producing a rectangular signal taking advantage of the inductance of...
We find this circuit in an old American documentation, but it is perfectly current by its...