setchell: Setchell Carlson 427 Pilot lamps

 I have aquired  a Setchell Carlson 427 equiped will two 47 pilot lamps as the eqiupment list states. I though 47 lamps were for dc votage but they are on an ac. They do light up very bright  but very dim after warm-up. Any thoughts as to why they are very dim or why dc lamps on a ac line?

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AC or DC doesnt matter for incandescent lamps like those dial lamps. When they are connected in the heater chain of an AC/DC radio, it is usual that they light up very bright at the first moment while the tube heaters are cold and have low resistance, but become more dim after a few seconds when the heaters are hot and have a higher resistance.  Some radios have some kind of current limiting device to give longer life to the lamps, it might be for example a NTC resistor in series with the heater chain or a PTC resistor in parallel to the lamps. 

It is clear from the schematic that the lamps will glow dimly in this radio. A #47 lamp is intended for 6.3 V 0.15 A . The current in this radio's heater chains is also 0.15 A but as the two lamps are in parallel and also shunted by a part of the rectifier tube 35Z5 's heater, each lamp will not get more than perhaps 0.07 A.

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Dim is for x10 life. Old 6V torch lamps were often closer to 4V as brightness mattered more than life, whereas long life 6.3V pilot lamps are x50 life if quite orange. The 12V car bulbs are really more like a 15V lamp.

Filament lamps don't care about DC or AC, only the true RMS voltage. They have even be used at RF.
One lamp is on RF and the other on a calibrated DC supply that is adjust till it's the same colour & brightness as the one on RF. Then the DC power = AC power.

If they are in series with the tube heaters then they are too bright till the heaters warm up as the room cold resistance is very low. Some sets, especially TVs on 200 to 250V had a thermistor to limit inrush current when cold. I can see on the schematic preview that the tube heaters are in series.
 

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thanks for the expanation 

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thanks for the explanation  

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