This battery-powered 3-valve circuit was found in American documentation from 1947; Two batteries are used, one high voltage and one low voltage for the filaments.
This circuit was found in a 1975 documentation. Operational amplifiers must have a symmetrical source and...
The circuit shown was suggested by Analog Devices (www.analog.com) in its Application Note AN-411...
This circuit was obtained in a 1978 publication. The operational amplifier must use a symmetrical source....