Vintage Nixie Clock Help

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1 month 4 days ago - 1 month 4 days ago #10552 by Ty_Eeberfest
That's rather interesting about the crystal and the manufacturer still being around cutting quartz after all this time. I have no clue why that crystal needed to be so big unless maybe it's repurposed into the clock form some really high powered application (???). I'm puzzled as to why they bothered to base the design around a crystal and associated resonant circuitry. Most clocks from the TTL era derive their timing reference from the power line frequency, which was a very accurate way to tell time until the standards were relaxed (on the N. American grid, maybe elsewhere) 10 or so years ago.

I suppose those 2 caps standing on end are filtering the +5V rail that powers all those lovely old TTL chips. They're probably due for replacement due to age but not involved in the immediate problem. EDIT - I meant the caps are due for replacement not the chips! I wonder what (if anything?) filters the +180 supply then. I see no likely looking caps in any of the pictures.

Before I drive myself crazy trying to reverse engineer the circuit from photos let's see what you get for an anode voltage reading. Low anode voltage is the only thing I can think of that would affect all tubes like that. Every tube appears to have its own 7441 / 74141 driver, no multiplexing, so we can pretty well rule out bad chips.

Look into it later when the dust is clearing off the crater.
Last edit: 1 month 4 days ago by Ty_Eeberfest.

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1 month 4 days ago #10553 by dannyv
Replied by dannyv on topic Vintage Nixie Clock Help
Yes, its the voltage. I'm getting about 60v when cathode is used to light a digit.
Also, is it normal for cathode to be getting around 20v when not in use?
Found a few yellow flat capacitors that are rated 10000 μF and 250v.

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1 month 4 days ago #10554 by dannyv
Replied by dannyv on topic Vintage Nixie Clock Help
Just re-read your replies. Need to measure anode voltage as you said. Will do another measurement later today.

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1 month 4 days ago #10555 by dannyv
Replied by dannyv on topic Vintage Nixie Clock Help
Still the same. Anode to ground is 60v.
Will investigate around the power input/power supply.
Thanks!

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1 month 3 days ago #10556 by Ty_Eeberfest
Yep, there's the problem! I can't tell much from the photos as to what HV power circuit consists of but its probably not real complicated. To answer your earlier question above, cathode-to-ground should read zero for a cathode that is turned on, and on the turned off cathodes may float up to 30 - 40 volts (more or less - hard to say).

Look into it later when the dust is clearing off the crater.

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1 month 3 days ago #10557 by Froula
Replied by Froula on topic Vintage Nixie Clock Help
Crystals can operate in fundamental or overtone modes. Most low frequency crystals like this are cut for fundamental operation. The lower the frequency, the physically larger the crystal blank within the holder must be. Typical CB crystals are in the 27 MHz range, where this is 100 KHz, very low, almost in the the audio range.

This site shows various crystal packages, including a 100 KHz unit in a CR-15 case, The dimensions are also quite large.

http://www.af4k.com/crystal_holders.htm

"CR-15/U - Crystal Unit, 3 pins - 1-5/8" X 1-3/16" X 2" tall.
3 pins are 1/8" dia. Two are spaced 1/2" apart. third pin
is offset by 7/8" from each other other two."

Don
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