On Thu, 2008-10-16 at 14:26 -0700, Jim WA9YSD wrote:
> For the Ten Tec Auto antenna Coupler Model 253 requires a 6.3 volt 150ma
> lamp CM4 is stamped on the side what does this cross reference to? 81 what?
> Thankyou for looking.
>
> Keep The Faith, Jim K9TF/WA9YSD
>
Another check is the color of the bead inside the lamp. I think the 47
which is 6.3 volt 150 ma T3-1/4 bayonet base has a blue bead. Made by
many makers in the past CM is just Chicago Miniature's prefix. It was
the dial lamp of choice in AC/DC AM radios using octal base tubes which
were made by the many millions in times well past. Its still a common
lamp.
Dropping the supply voltage to half the lamp rating will increase the
lamp life immensely. According to a GE lamp book I have, lowering the
lamp voltage by 5% cuts the visible light output by 10% and doubles the
life. Repeating that in a geometric progression to half voltage gets a
very dim light but about 100 YEARS of life which explains that dim lamp
that is that old but still working in a San Francisco fire house.
At Collins for broadcast gear we wired a series resistor to each lamp
socket selected to lower the lamp voltage by 10% on type 327 lamps
(short lived at best) and then I found the 387 with the same voltage and
current but much longer life. But we left the resistors in place. I like
the resistor idea because the series resistor limit the peak current
when power is applied to the cold filament. Remember the filament
resistance when cold is 15 times lower than when hot, so unless the
supply circuit limits the current that turn on current surge is 15 times
the operating current. That is why lamps most often fail the instant
they are turned on.
73, Jerry, K0CQ
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