Re: Is this IN-18 bad?

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8 years 5 months ago #2995 by mathewbeall
Hi Folks,

I just got a batch of (6) IN-18 tubes and one of them displays this odd purple color only when the #1 segment is lit up. Is this something that will go away with time or should I have the person send me another IN-18 to replace this one?

Much Thanks,

Matt
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8 years 5 months ago #2996 by GreyFox
Replied by GreyFox on topic Re: Is this IN-18 bad?
I have one like that - its a replacement tube and I have the blue dots on the #1 only. From what I understand it indicates that the tube is over driven. Or it has too much power driving the digit.

Let there be neon light!

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8 years 5 months ago #2997 by mathewbeall
Replied by mathewbeall on topic Re: Is this IN-18 bad?
That is odd - it doesn't happen with any of my other tubes in that socket - which would lead me to believe that it isn't an issue with overdriving.

Matt

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8 years 5 months ago #2998 by Nocrotec
Replied by Nocrotec on topic Re: Is this IN-18 bad?
Hi!
This is the well known Blue Spot problem!
Here is the description I sent to Brian today:

The blue spots are caused by the following circumstances:
If low voltage drivers are used, as example the 74141 drivers, the cold cathode voltage (non glowing cathode voltage) drops down to the clamping voltage of the output transistors (70-100 Volts).
In this state the mercury slightly breaks down, slightly ionizes, and little current flows from the anode, through all 9 non glowing cathodes through the Z-Diodes (Driver protection diodes) to ground. And that
inonized mercury can be seen as blue spots in the tube.
That's all.
;-)
How to avoid it?
Don't use any off cathode clamping voltage, but high voltage drivers.
And again, for the thousandth time: YOU CAN NOT DRIVE ALL IN-18 TUBES WITH 74141 DRIVERS!!!! SO DO NEVER USE THEM!
IF A BLUE SPOT APPEARS IN YOUR IN-18 TUBE THE CIRCUIT IS WRONG, NOT THE TUBE!
Look here:
www.nocrotec.com/shop/product_info.php/l...Dream-Nixie-Uhr.html
Dieter

If you are in a rush, walk slowly!
www.nocrotec.com
The following user(s) said Thank You: Stuckey

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8 years 5 months ago #2999 by mathewbeall
Replied by mathewbeall on topic Re: Is this IN-18 bad?
Ahhhh - ok... I will try this tube in another clock I have that doesn't use those drivers to validate.... thanks for the information!

Matt

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8 years 5 months ago #3001 by GreyFox
Replied by GreyFox on topic Re: Is this IN-18 bad?
Bad circuit - Hmmmm my kit is one from tubehobby and the tube there that outgassed worked just fine. The replacement IN-18 has the blue dots for the #1 digit. So am I now faced with a bad circuit or a tube that is again out gassing?

Maybe I should switch kits ag go with a different setup.

Let there be neon light!

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