Musical doorbell (CB9210E)

This musical doorbell was found in a Popular Electronics from the 90s. The U4 melody generator integrated circuit is uncommon today.

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X100 amplifier with the L161 (CB9011E)
This circuit is from old documentation. The operational amplifier is uncommon nowadays. The...
TTL Memory 7400 (CB22412E)
This memory flip-flop must be powered by 5V voltage. The circuit stores 1 bit. ...
CK722 Preamplifier (CB22536E)
This simple preamplifier was published in Radio Electronics magazine in February 1958. The battery...