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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2 transistor radio (CB20517E)
This circuit with germanium transistors was found in documentation from the 50's. The transistors are...
Old Phase Shift Oscillator (CB13956E)
The circuit presented was found in a documentation from the 1950s, generating a sinusoidal signal...
VHF Preamplifier (CB19599E)
This circuit was originally indicated as a signal reinforcement step for the previous receiver...