This circuit with current up to 100 mA according to the transformer was found in the Radio Electronics magazine of October 1991. The regulation is done directly by the zeners.
This is 4-input audio mixer using an integrated circuit 741 and two more operational amplifiers....
We found this configuration in documentation from the 1970s, but all components are current. If a...
Found in a 1980s American publication for amateur radio this circuit uses components from the era. The...