PH meter (CB20731E)

This circuit was obtained in an old American documentation. The integrated circuit used is uncommon today. Modern equivalents can be searched.

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Conductance Adapter for Multimeter (CB26013E)
With this circuit it is possible to add a conductance scale to a common multimeter. The circuit was...
Successive Tone Decoder PLL (CB3958E)
This circuit with the known PLL 567 can be found in other versions in this section and in this...
Transistorized Voltmeter (CB18582E)
This transistor circuit was only found in documentation from the 1960s. The original transistor is made of...