IN-18 and PIRs

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3 years 9 months ago - 3 years 9 months ago #9306 by Torsten Lang
Replied by Torsten Lang on topic IN-18 and PIRs
Hi Ian,
I checked my Blue Dream after it turned on this afternoon. The tubes are just getting hand warm as I would expect with about 0.6W heat dissipation.

I've taken a look into the Spectrum schematics. If the power supply really provides 170V the tubes themselves cannot get hot. The currents should even be lower than in my Blue Dream.

But what I've seen is that the high voltage drivers are operated way beyond the operation conditions given in the data book. They use "high voltage" logic and are specified for 10.8V..13.2V. Operating them with 5V is way beyond the spec.

I searched for an old Supertex datasheet to check if Microchip has taken over the data correctly - both the databook I found and the current datasheet are consistent. I don't know what the consequences of this design fault are...

With best regards,
Torsten
Last edit: 3 years 9 months ago by Torsten Lang.

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3 years 9 months ago #9309 by Ty_Eeberfest
Replied by Ty_Eeberfest on topic IN-18 and PIRs
I've seen that "trick" of running Supertex chips out of spec somewhere before. At the risk of committing blasphemy I'm going to say I THINK it was in one of Jeff Thomas' designs, which would suggest there is some validity to the trick since Jeff was never one to do anything half assed. For my own direct drive designs (including the IN-18 clock I was talking about above) I didn't want to take chances so I run my Supertex chips at Vdd = 12v and the signals from the Atmega are level shifted to 12V by a CD4504B chip.

I disabled PWM on my IN-18 clock so the tubes are running on pure DC at full power / brightness. After a warm-up period they are a little bit warm to the touch. Using my 25 year old Fluke non-contact temp probe I read 32.2*C at the hottest point on the tubes. The room is 21.1*C. Nothing is making noises.

To clarify details of my circuit (and yes I can hear some of you cringing because it's not exactly to specs!) I checked a few things. For some reason my HV generator is producing only 163V under load and same on open circuit. My anode resistors are (gasp!) 3.9K. Dropping 25V across the resistors, 138V across the tubes. Current is 6.4mA. Tube dissipation should then be about 0.88W. Tubes look nice and bright, no sign of any blue tint and of course no arcing. The tubes are 04-85 date codes which any "IN-18 purist" will say are "bad" date codes (nothing before 1990 is any good, they say).

I arrived at the 3.9K resistors through experimentation when I first built the clock. With the more conventional 10K or 6.8K resistors the tubes were not very bright and they would develop severe cathode poisoning (even on the very active seconds digit) in a matter of a few days. I'd have to take them out and cook them until they screamed for mercy on my "tube healer" rig. Then they would be okay for a few days only. The tubes I am using today are the same tubes, Once I increased the current enough all my troubles went away - the tubes are fine.

I have one Russian data sheet and one English data sheet that say IN-18s should be run between 4mA and 8mA. Then I have another English data sheet that says 4mA is the maximum. Hmm.

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

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3 years 9 months ago #9315 by Pacman223
Replied by Pacman223 on topic IN-18 and PIRs
this is all very interesting.. apparently IN-18 tubes are much more difficult to design around ..

My first thoughts .. doesn't nixie tube do better with higher voltage like 200v.. + a higher resister.. ??

Ty's 3.9k resister + 163 volts.. I wonder if my original assumption is correct after all .... at least for IN-18 tubes.

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3 years 9 months ago #9320 by judge
Replied by judge on topic IN-18 and PIRs

Pacman223 wrote: this is all very interesting.. apparently IN-18 tubes are much more difficult to design around ..

My first thoughts .. doesn't nixie tube do better with higher voltage like 200v.. + a higher resister.. ??

Ty's 3.9k resister + 163 volts.. I wonder if my original assumption is correct after all .... at least for IN-18 tubes.


The reason for running tubes with a higher voltage is that it reduces the effect of differences between tubes and individual digits in terms of maintenance voltage and current - so you would get a more even glow across tubes and digits.

When a datasheet specifies the strike voltage, it means the voltage at which all tubes and digits are guaranteed to light. Most tubes will light at lower voltages than that, depending on the circumstances in which they are lit - it is harder to strike a tube in the dark for example (ambient photons can provide the initial ions in the tube that are needed to start the ion cascade that causes the glow). Indeed, most tubes I have will happily light right down to the maintenance voltage. Of course, driving the tubes at these low voltages makes the issue I mentioned in my first point much more noticeable.

One possible issue with IN-18s is that they are more demanding of the power supply. To run at 6mA, you need a power supply that can happily feed a clock with 36mA at whatever voltage was chosen. At 170V this means it can produce 6.12 watts. At 200V that would have to be 7.2 watts.

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3 years 9 months ago #9348 by judge
Replied by judge on topic IN-18 and PIRs
Over in this other thread , Ty gives a link to Dieter's IN-18 clock . There is this paragraph:

"The switching power supply generates 150 volts DC"

And the anode resistors are 1.8K.

These clocks have been running for years...

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3 years 9 months ago #9350 by Ty_Eeberfest
Replied by Ty_Eeberfest on topic IN-18 and PIRs
Thank you Judge!! I totally overlooked that info - guess I should read my own links more thoroughly, That pleases me to see a Dieter design that is more in line with what I did than with the prevailing "Internet wisdom". I was starting to doubt myself a little bit in spite of my design's good operating record.

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

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