Active three-tone filter (CB20808E)

This circuit was found in an American documentation and can be added to common amplifiers of any type. The transistor can be any general purpose.

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Overvoltage protection (CB8360E)
Found in a 1960 General Electric documentation, this crowbar circuit blows the fuse in case of...
Crystal Tester (CB24174E)
This circuit was originally designed for testing crystals used in color televisions, but it works...
Test circuit with bridge (CB22530E)
This bridge-biased transistor test circuit measures gain in the range 0 to 300. Circuit is from...