[Patrick]

I always power up radios with a dim bulb tester on my variac. I have noticed that with certain high tube count radios, that the 100W bulb will glow dimly. But with the 16, the bulb only glows dimly up to around 90 volts. The radio does play. When I increase the voltage to 120, the volume, naturally, increases, but the bulb gets really bright.


Doesn't the wattage output of the radio determine how bright the bulb gets? If that's true, then is the wattage output of the 16 high enough to cause the bulb to glow bright, or do I have another problem?

[Phlogiston]

Power output is insignificant as compared to power consumption.

Look at the rating for power consumption on the radio. Anything greater than 120W is going to make the bulb bright - and - consider this - placing a 100W bulb inline with, say, a 600W (big) radio is going to cause a voltage drop even at line voltage - see Ohm's Law.

[Patrick]

Got it. And the power consumption on this radio is 130W. Thanks.

[Patrick]

Just re-read Philco Phil's explanation of the dim bulb tester, whereas the bulb wattage should be 1 1/2-2 times the radio's wattage. Should have read that before I asked the question, but maybe other people can benefit from this as well. So ideally I should have used a 200-300 watt bulb. Or just power up slowly with the variac, watching the ammeter, since at 120V, and 130 watts, it should draw 1.08 amps. It was playing fine, but weak, at 90V with the dim bulb tester in the circuit.

[Eliot Ness]

Yes, when I power up using a variac and ammeter I never use a dim bulb with it, but I guess it adds another layer of safety against burning out a xfrmr.  You just have to be aware of the voltage drop.