This circuit was found in documentation from Analog Devices. The circuit is based on an AD795 and a commercial pH probe.
This amplifier, found in a 1980s documentation, should be powered by a symmetrical source. Modern...
This is a voltmeter with high input resistance. The transistor is germanium. We found it in an...
Up to some minutes intervals can be obtained from this circuit. The circuit can use a lamp (or...