[Arran]

  The use of a tuning light is interesting, Rogers, Canadian Majestic and DeForest Crosley radios used to have a feature like that up until 1936 or so. The lamp is a 25 volt bulb, and it dims when you tune into a station, really dims on a strain station. I will have to study the circuit again but I think it's connected to either the bias circuitry or the AGC, some of the higher end models like the Rogers 10-12 have an extra tube as an amplifier to power the tuning light. It's curious that Philco did not incorporate this feature into more of their sets, it would have undoubtedly been cheaper to use then the shadow meters, more reliable, and they still would have avoided making their sets RCA like by not using a magic eye tube.
Regards
Arran