Hi Jim,
Since Marinus' first post referred to a Ten-Tec 228 tuner, you are
correct about the 12 to 14 volt supply. Marinus also mentioned the bulbs
in his Omni 546-C, and asked whether they are 6 volt lamps. I am not
familiar enough with the 546 to speak on the pilot lamps it uses. I do
have a Omni VI 563, and a manual for it.
The Omni VI 563 uses pulse width modulation to control a regulator
circuit that determines the meter lamp brightness. The manual says that
the lamp voltage varies from about 2.7 to 5.7 volts. I have not found a
part number in the Ten-Tec manual for the bulbs, though I suspect they
are number 47 bulbs, commonly used in tube radios with a 6.3 volt
filament supply. With only 5.7 volts maximum supplied to a 6.3 volt (I
am guessing) bulb, you should already be getting extended life from the
bulb.
I like to buy bulbs from Mouser. They have a good selection of Chicago
Miniature lamps, and you get a price break at ten units. Interesting to
compare the 47 bulb with the 755. They have identical voltage and
current ratings, yet the 755 produces less light (0.330 M.S.C.P. versus
0.500 M.S.C.P. I'm not sure what M.S.C.P. is. Perhaps mean spectral
candle power?) and lasts almost seven times as long. It also costs
almost twice as much.
When running incandescent lamps at various voltages, the light they
produce does not merely change intensity. The spectral distribution of
the light also changes. Running at a reduced voltage lowers the
temperature, and shifts the emission towards the longer wavelength,
redder end of the visual spectrum. When television studios get more
sensitive CCD cameras, requiring less light, they cannot just dim the
existing lights. They have to get new lamps to maintain the same color
temperature at a lower light level.
Ken N6KB
Unless the stock bulbs are 6.3 volt lamps
The lights are wired in parallel and run on whatever power supply is
plugged into the RCA connector on the back. For most of us, that's
12-14 volts.
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