Metal locator (CB7506E)

This simple metal detector was found in a 1960 Sylvania transistor manual. The phone must be high impedance or crystal.

Capacitance Compensated Amplifier (CB3947E)
This circuit was obtained in a manual of the used old operational amplifier. However, the same...
Gain 100 Inverter Amplifier LM3900 (CB4505E)
Other series amplifiers such as the MC3301, MC3401 and LM2900 can be used on this circuit. We...
Battery Condition Indicator (CB4984E)
The circuit is from an 80's publication, but the components are current, only special type diodes...