Brad,
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If I can recall the neon-photocell approach was very similar to that used in the HP 5245L counter series display boards.? If you can find an old board (base P/N 05212-6016) you might have some luck in finding similar photocell devices.? The suffix to the part number (¡°Series 6xx¡±) changed reflecting the board functionality.? There was also changes in the design of these boards where they either contained an enclosed module termed ¡°Decoder¡± (One HP part number is 1820-1683¡±)? or a ¡°Photoconductor Plate¡± where the photocells directly drive the Nixie tubes.
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It appears that HP changed to the ¡°Decoder¡± module in later model counters.? It is a black plastic enclosure on the board with a removable cover but I have never opened one up to see what is inside.? Given its construction I am assuming that it, too contains photocells.
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Greg
