I used to own a 1936 RCA 9K Console Radio with Magic Brain and Magic Eye.
see here:
http://www.worthpoint.com/worthopedia/r ... sole-radio

It had wonderful tone and I've wondered what it would be if
one built a radio section to tap into the amp section.

If my memory is correct, they used what is called a "Air Variable Capacitor" for the tuner.

I just thought, gee, that sure would be cool to be able to use your guitar amp as a old timey radio receiver amp -

AM/FM/Short Wave, Turntable.... you get the idea

There are also tube amps with taps for ipods and mp3 players.
it gets me thinkin' sometimes.