Metal locator (CB7506E)

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

Power Voltage Follower with the 741 (CB11885E)
With this configuration we have a voltage follower, amplifier with unit gain, in which the output...
Sample and Hold (CB11542E)
This circuit is from the Linear Circuits Application of Texas Instruments, using an operational amplifier...
High impedance instrument amplifier (CB15801E)
This amplifier, suggested by National Semiconductor (Now Texas Instruments), has high input...