Ammeter (CB9660E)

This current meter with many scales was found in a 80s American documentation. The operational amplifier is from that time, uncommon nowadays.

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Adjustable High Q Notch Filter (CB15815E)
We can implement this filter with more modern equivalent operational amplifiers, since the LM110 is...
Simple Stethoscope (CB18347E)
This stethoscope or amplifier for hearing aid using a crystal headset and microphone was found in a...
Divide-by-16 Counter - 4520 (CB176)
The normal use of a 4520 as a divide-by-16 counter is shown in Figure bellow. In the normal...