On Tue, 2008-10-21 at 03:39 -0700, Jim WA9YSD wrote:
> The 755 has an average life of 20K hours according to the Sylvania Lamp
> replacement book. I did an online search and I find this contradicting.
> I am not sure if Ten Tec added a resistor or not add one in the circuit. if
> they . I did not look that far into to it.
> I started out looking for a lower current 6.3 volt bulb with long life. The
> 755 6.3 volt 150 ma T3-1/4 bayonet base had long life but equal current.
And much lower light level.
> The only problem was I could not read the last number cause when the soldered
> the bulb CM had solder over the last number on both stamps never the less.
> You see I bought this equipment used and I do not know what was originally
> put in it. Is it a 47?
> Keep The Faith, Jim K9TF/WA9YSD
The 47 would be a very likely candidate as it was used for literally
millions of AC/DC radios and almost every tube radio. Since what is
there is that size and has the white bead of the 47 that's what you have
now. Back in the 40s and 50s we had screw base and bayonet base, round
bulb and tubular bulb and the makers more often told them apart by bead
color than by part number. Then as manufacturers got more formal and
wrote more specifications, a greater variety of lamps were made and the
five criteria of base, glass shape, and bead color were not enough to
identify the lamps in the service shops so the numbers became more
prominent with several selections at each voltage and current for light
vs power consumption. As an indication of its popularity, the 47 in my
Mouser catalog is the cheapest lamp of that physical size yet today.
Going to a lower current lamp will lower the light level. You can
accomplish a similar result by going to a 12 volt lamp running on 6.3
volts with a 756, 1815, 1893 or several others. Running at half voltage
the lamp life computes out to about a century if it was 1000 hours at
rated voltage. What is the supply for the lamp? A wall wart? unregulated
or regulated can make a huge difference in lamp life. The voltage
regulation on an unregulated wall wart can be a definite limiter on lamp
life (running high voltage).
And then there are the LED replacements that are possible, most of which
demand DC and may only put light out the end of the lamp which limits
Is there any indication in the manual (that you have or could download
from TT) of what lamp was intended? I think that if I had designed the
unit, I would have allowed used of 755, 47, 44, or 51 and said so in the
manual with a hint of the trade offs between them on power consumption
and light output. 755 has the least light output and efficiency, 47 has
more light, 44 more light, 51 I forget its ratings now, but its much
harder to find these days.
Going to a manufacturer's lamp book is handy but going to a distributors
catalog will show what lamps really are available. Most distributors
don't stock the full lamp book's variety of lamps.
The 1893 is used in a lot of Grote clearance lights for trailers and
trucks so is often available at truck stops and car parts stores.
73, Jerry, K0CQ
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