This 4-transistor amplifier can work from 4.5 or 6 V power supplies. We found it in a Mullard transistors manual from 1960. The transistors are from the time.
We found this circuit in an American documentation of the 80's, being indicated for the test of...
This amplifier for instrumentation with differential input is from the factory manual of the...
This circuit is from old technical documentation, used to monitor the voltage of a 12 V battery. The...