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RCA 816k Console Radio, circa l938  c.l999 catskillki  
oUseful also for slicing eggs, this very precision bank of aluminum plates is used to tune the radio.  Three sections of the fingers would interleave to vary the capacitance and hence the frequency of the local oscillator as well as resonating the input frequency from the antenna.

Manufactured to a few thousands of an inch tolerance, these cumbersome and trouble prone mechanical contrivances have been replaced by solid state varactor diodes, voltage-dependant capacitors, and phaselocked loops.
Listen to WBCQ, shortwave at 7.415 mHz , Kennebunk, ME