I obtained a "77M The Tracer" made by Progressive Electronics at my town's recycling center. It even works. I only have the tone generator, continuity tester, part of it. Inside is a 4049 and many, many capacitors, diodes and resistors.
I'm too lazy to trace it out ;-) so I'm looking for a schematic. I tried Google but only got sales pitches for the current versions.
There is an external switch which controls the functionality. It can trace continuity by illuminating an LED or it can send a warbling tone. The same two leads are used for both functions.
Nice compact design.
Al