Rumble filter (CB6541E)

This turntable filter was found on an 80's Elektor. The circuit makes use of operational features that are easily obtainable today.

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Full wave slave control (CB8156E)
Using SCRs, this circuit from a 1967 General Electric manual allows full wave load control with SCRs....
Sound Strength Meter (CB12930E)
This interesting circuit from a publication from the 1970s, measures the intensity of the sound...
Simple Transistor Tester (CB19460E)
This simple NPN and PNP transistor tester configuration can use the low current range of a common...