Vintage Heathkit AC-11B channel separator, vacuum tube multiplex adapter for HI-FI FM stereo

Vintage Heathkit AC-11B channel separator. This is a vacuum tube multiplex adapter for converting a FM mono signal into a stereo signal. It measures about 10" x 3 1/2" x 3 1/2".

We plugged it in and it powers up. We didn't test it further.