This sensitive 4-tube, battery-powered receiver was found in a 1949 Radio Electronics. The circuitry was wired in crystal earphones.
Using a 12 V transformer, this unit can provide a much higher output voltage. The circuit is from a 90’s...
Found in Linear Technology documentation from the 1980s, this circuit has an accuracy of 0.01%....
This circuit was found in a 1967 EEE. The transistors are from the time and can be tested...