Photo-Electric Relay
  This photoelectric relay was made by  G-M Laboratories, Inc. as catalogue number 1224, and sold by the Chicago Apparatus Company.

   The vacuum photoelectric tube
is at the left on the wooden breadboard, and has the usual cylindrical cathode half- surrounding the anode wire. The signal from the anode leads to the control grid of the [missing] type 46 tetrode vacuum tube. The plate current drives a small relay, which, in turn drives a larger relay. The tall black cylinder at the right with the perforated cover is a ballast resistor.

The date of the apparatus is probably mid-1930s. It is in the Greenslade Collection.

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