This amplifier with fixed AC bias was found in a 1947 documentation. The circuit uses two transformers in the power supply and two full-wave rectifier tubes.
Books and e-Books by Institute NCB 100 CIRCUITS - SHIELDS FOR ARDUINO FUN PROJECTS FOR THE...
The LM109 was manufactured by many semiconductor companies that presented different configurations in their...
This shield was found in an American documentation from the 70s. The operational amplifier is from...