Digit Brightness, Classic Rev6, IN-8 Tubes

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6 months 3 weeks ago #12778 by Ty_Eeberfest
Hi Torsten, I was just thinking about you ;)
I've never seen the pulse mode specs for this particular tube before. Apparently I've been working with an incomplete datasheet. I didn't know there were published specs for pulse mode but now I've found a 4-page version (3 pages in Russian, page 4 in English) that seems to be complete. Probably the same one you are using.

As you can see from reading the discussion, none of us can figure out why Jedidiah's clock looks dim. One thing I've learned from recent experimentation is that there is definitely some non-linearity in the relationship between current, voltage and brightness. I'm not sure if the brightness non-linearity is a tube characteristic or a human eye characteristic though. I have no way of measuring actual light output.

Jedidiah, here are a couple things I should have brought up sooner:

Am I correct in thinking you have 2 of these clocks? If so, how does the brightness of the clock in question compare with your first clock? Are both clocks socketed, i.e. can you swap tubes between clocks? Comparing multiplexed tubes to multiplexed tubes would be more meaningful than comparing to a direct (over)driven tube.

Did the tubes come from a trusted source? Are they definitely NOS and not used "pulls"??

I've linked the data sheet with the pulse mode specs below in case anyone needs it...

www.tube-tester.com/sites/nixie/dat_arch/IN-8.pdf

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

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6 months 3 weeks ago - 6 months 3 weeks ago #12779 by Torsten Lang
Hello Ty,
I first found the pages at tubehobby.com , but the content is the same.

I looked around to find any hint clarifying the relation between current and brightness. At least in an old publication by William G. Miller there is a hint that it is linear And there I also found the power of 3 relation with the lifetime again.
Last edit: 6 months 3 weeks ago by Torsten Lang.

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6 months 3 weeks ago #12780 by Jedidiah
Hi Ty. I can understand how you might think this is an Arduino shield, but I assure you that it is indeed a Classic Rev6 piggy backed to a tube board I designed. The attached photo of the underside should clear it up for you.

Also, when you switch your tube anode resistor to 1.5k, give it about 30 seconds and then measure the voltage drop across it and calculate the current. In my case, when I did this, the voltage drop settled in at 1.9 volts across the 1.5k resistor, for a current of 1.27 ma, very close to the current with the 3k resistor.

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6 months 3 weeks ago #12781 by Jedidiah
Torsten, if I use a 30k resistor in the direct drive setup, this results in about 1.2ma, and the tube brightness is then comparable to the clock tubes.

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6 months 3 weeks ago #12782 by Ty_Eeberfest
Okay I see shat you did there. Looks amazingly similar to an UNO under an All in One from a distance.

I assure you I have left the resistor at 1.5K for more than 30sec. More like 30min to 2hrs. When I switch back to 3K after those long periods of 1.5K the brightness still steps down or IOW it is not fading after 30sec.

Take another look at Torsten's first post and get/read the data sheet he links in his second post. I don't know which data sheet you have been using but the one I have been using (at very bottom of this page) turns out to not tell the whole story. Using Torsten's data sheet we see we are operating the tubes in "Mode B" (the anode pulse duration tells us this). In Mode B the maximum peak is only supposed to be 5mA (.83mA average). By that standard the tubes are already being slightly overdriven by the ~7.5mA peak / ~1.2mA average that the stock resistors produce.

Note that 2.5mA that we've been talking about is actually only acceptable for direct/continuous drive. The 15mA peaks needed to get 2.5mA average on a 6 digit MUX clock are an absolute no-go, So says the data sheet.

So I'm not seeing why we should drive the tubes even harder. It'll add just a little more brightness at the cost of heating up the tubes and decreasing tube lifetime dramatically. (One source I looked at today but can't seem to locate again right now said tube life decreases by the cube of the amount of overcurrent. That's a lot.)

Still waiting for you to tell me if you can switch tubes around between your UNO clock and your Rev.6 clock. Yes, I am raising the possibility that there is something wrong with the tube set you're using on the Rev.6 ... mainly because it's about the only thing we have not (to my knowledge) looked at.

BTW you probably don't know Torsten, He is not here very often but when he does post I pay attention. He has a different way of looking at things and has given a lot of good observations in the past.

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

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6 months 3 weeks ago #12783 by Torsten Lang
OK, that confirms that there is nothing unusual going on with the multiplexed tubes.

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