According to the Chicago Miniature listing in the print Mouser catalog
at hand, the 47 is rated for 3000 hours and the 755 is rated for 20,000
hours. The 47 puts out a half spherical candle power and the 755 a third
using the same 150 milliamps.
The 47 life could be extended while lowering the current requirement by
adding a series resistor. Rule of thumb for lamps is that lowering the
lamp voltage 5% cuts the light by 10% and doubles the life. 24,000 hours
is 3 doublings of 3000. So you cut the lamp voltage by 15%, the light by
30% (neglecting the geometric progression) and get 24,000 hours.
Amazing, that's the light output of the 755.
73, Jerry, K0CQ
<SNIP>
>
>
> According to Garey - K4OAH, who is an expert on Drake equipment (if
> you are on the Drake list, you are very familar with him and his
> expertise), if you replace the number 47 bulbs with number 755
> instead they will last the life of the equipment. In my case it was an
> SPR-4 receiver, but I expect the lifetime of a Titan III would be
> about the same.
>
> Geoff.
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