High impedance millivoltmeter (CB20611E)

We found this circuit in an old American documentation. The components are from that period and may present difficulties in obtaining them.

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Limiter with zener diode (CB7054E)
This circuit was found in an old Electronic Design. It makes use of sidacs and operational not very...
Four Way Call Warning Light (CB17693E)
This 2009 circuit is a bilateral call warning. Easy to build, using light communication between two...
Speed and direction control for shunt motors (CB5418E)
This circuit for shunt motors was found in an American 1980s documentation. The SCR should be rated...