This interesting digital counter with relays with complementary outputs was found in the Radio Electronics magazine of October 1961. The supply voltage is in accordance with the relays used.
This amplifier for hearing aid was found in a 1968 documentation using an integrated of the time....
We obtained this circuit from a 1993 documentation. The circuit has 9 current ranges that are...
In the figure we have the transmitter of a data transmission system with optical fiber suggested by...