, although a trademark of the Burroughs Corp
, is the generic
term for cold-cathode
indicator tubes. Basically, a neon
tube where the numbers to be displayed are actually metal electrodes
shaped like the number itself. The result is an easily readable, nice, non-flickering orange or red/orange light in the shape of a number, reasonably visible in daylight.
Manufactured primarily in the 1960s
, and based on the same technology as the vacuum tube
, they are no longer made but remain in large quantity, and are consequentially not difficult to obtain.
The characters in early models were all 0.3"-- 0.6" digit height and visible from the top/end of a bulbous glass
envelope. They eventually became available in a range of sizes up to 2", and later more commonly seen with the stack of digits viewed from the side of the tube, in a conventional miniature radio tube T5 outline. One undesirable aesthetic concern is that since the digits are stacked front-to-rear, un-lit digits partially obscure the lit digit, and the digits seem to shift back and forth as they change, since the stack of digits is about a quarter-inch deep.
Strangely, they are a collector’s item
with a virtually limitless storage life. In normal use, they last for 20 to 50 years provided they are properly cared for. This includes not operating them at excessive current
s (in which case the electrode
s slowly evaporate
and blacken the bulb), and illuminating the cathode
s periodically to prevent cathode poisoning
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