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I set up a test circuit using TTL components and 74141 Nixie driver to
count from 0 to 9. The HV source I have is adjustable up to 200V
output. I get good illumination of all digits if I use a 26K anode
resistor, with a voltage of 181V. The loaded voltage measured after the
resistor is ~136V and the current measured between the anode resistor
and the tube is 1.7-1.8 mA. If I crank the voltage to 200.0V the
current between the resistor and the tube cathodes is ~2.5mA. The
digits look sharper and brighter. The voltage after the resistor is ~
137V. My questions are: 1. To get maximum tube longevity, should I
measure the voltage before or after the anode resistor? 2. Am I
measuring the current correctly between the anode resistor and the tube
cathode? The data sheet for this tube states: Firing voltage no more
than 170V, working current digits (2.5-4.5 mA). Stated longevity no
less than 10,000 hours if Voltage ≤ 200V and anode current for
digits ≤ 2.5 mA. But there are 8,760 hours per year and this
would mean the tubes would fail before two years of continuous use.
Others have stated that the life -time of these tubes can be for a
decade. I assume that this is due to running the tubes at lower
currents and voltages. 3. What would most of you run these tubes at
voltage and current? 4. Does it matter what Voltage and anode resistor
combination as long as the cathode current doesn't exceed 2.5 mA?

[edited by A.J. - please trim quoted material]
On Tue, Aug 10, 2010 at 3:49 PM, DanielK <kuriloff@...> wrote:

The HV source I have is adjustable up to 200V output. I get good
illumination of all digits if I use a 26K anode resistor, with a
voltage of 181V. The loaded voltage measured after the resistor is
~136V and the current measured between the anode resistor and the
tube is 1.7-1.8 mA. If I crank the voltage to 200.0V the current
between the resistor and the tube cathodes is ~2.5mA. The digits
look sharper and brighter. The voltage after the resistor is ~137V.

<snip>

Does it matter what Voltage and anode resistor combination as long as
the cathode current doesn't exceed 2.5 mA?

Go ahead and leave the supply voltage at 200v, as others have stated here
that will not hurt anything and will allow the nixies to ignite well into
their old age. In general, the supply voltage of nixies does not matter
(within reason). The famous Mike Harrison clock drives them at 250vdc, and
works great.
The value you should be worried about when driving nixies is the current.
You always should drive nixies to within their spec, never drive them at
less than spec. If you do, you'll find that your nixies fail after about a
year of cathode poisoning (YES, I learned the hard way). I recommend driving
IN-8's, IN-14's, IN-8-2, IN-12's at about 2.5ma. I have IN-14's that have
been running 24/7 for about 8 years now, although I have definitely seen a
few bad tubes that failed after only a couple of years. Your mileage will
vary.
Welcome to the hobby! Nixies are a lot of fun.

-Adam


[Non-text portions of this message have been removed]

"DanielK" <kuriloff@...> wrote:

The voltage after the resistor is ~ 37V.
My questions are:
1. To get maximum tube longevity, should I measure the voltage
before or after the anode resistor?
2. Am I measuring the current correctly between the anode
resistor and the tube cathode?

data sheet:
Firing voltage 170V max
working current digits (2.5-4.5 mA).
longevity no less than 10K hrs if Voltage (less than ?) 200V
& current (less than ?) 2.5 mA.
(ref: 8,760 hrs/yr => 2yrs life, 24-7)

3. What would you run these tubes at (V & mA) ?
4. Does it matter what Voltage and anode resistor
(are as long as the) current doesn't exceed 2.5 mA?

Here's a little drawing I made last year, on the basics of nixies:



1. Both measurements are used. One is the supply voltage (Vsup), and the other is the 'tube drop' (VA). The difference of the two divided by the anode resistor, determines the current flowing thru the tube. For all practical purposes, the cathode and anode current are the same, because only one cathode should be conducting at any time. There is some leakage from the unused cathodes, but usually the combine leakage is only a tiny fraction of the current flowing thru the selected cathode.

The supply voltage is what is used for the strike voltage, since before the tube strikes, no current is flowing, and therefore there is no voltage drop across the anode resistor (RA), so VA & Vsup are equal, before the tube strikes. Once it strike, the difference develops, as a result of current flowing. There is also a finite time over which this action occurs. I've measured in ballpark of 10 to 50uS (microseconds).

2. Anywhere in the path is valid. You really don't even need to use the current meter. Just measuring the voltage across the anode resistor, and dividing that difference by the resistor value, will give you the current. I rarely use the milliamp and amp selections on my meter. Again, with only one cathode On at any time the anode and cathode current can be considered equal.

3 & 4. The current is what you should be looking at. The voltage need only be high enough to ensure that the tube strikes. 170V or greater. 180V is commonly used, because it has a 10V of margin. You can use higher voltages if you like. It becomes more important if you are multiplexing the tubes. The higher the voltage, the more quickly, the tube strikes. A tube that strikes in 50uS at 175V, may strike at 30uS at 190V. Nixies usually have a specified current range, and for good reason. Life decreases as the current goes up. But also important, if the current is too low, the tubes may develop 'cathode poisoning' because they aren't able to drive off metal that's been sputtered onto them, from a previously ON nearby cathode. Personally, I would operate it just at the minimum specified current.

On Wed, Aug 11, 2010 at 1:49 AM, DanielK <kuriloff@...> wrote:

137V. My questions are: 1. To get maximum tube longevity, should I
measure the voltage before or after the anode resistor?

Nixies (just like any gas cold discharge devices) behave in a manner
similar to Zener diode, i.e. the they are adjusting current while
trying to maintain the voltage constant. That is, measuring the
voltage at cathode-anode interval is kind of meaningless. It's current
what matters.

2. Am I
measuring the current correctly between the anode resistor and the tube
cathode?

Looks like you don't. If the resistor is connected to the anode lead,
then you break this connection and insert your ammeter in series with
the resistor and the tube.

If you can read Russian, then please study pages 87-90 in [1] for more
details on the theory. Google finds an electronic copy at [2].

Dmitri

[1] А.М. Бонч-Бруевич, Применение электронных ламп в экспериментальной
физике, ГИТТЛ, 1956.
[2]

Great little diagram:
Question though, if you are solving for Ra you need to know this internal Anode Voltage correct? I have never seen this spec listed for tubes. I have always approximated the value for Ra and adjusted it until I got the current across the tube right. Is there a way to determine this optimal drop and thus solve for Ra??

--- In NEONIXIE-L@..., "Mike" <mbarile2@...> wrote:

Great little diagram:
Question though, if you are solving for Ra you need to know this
internal Anode Voltage correct? I have never seen this spec listed
for tubes. I have always approximated the value for Ra and adjusted
it until I got the current across the tube right. Is there a way to
determine this optimal drop and thus solve for Ra??

Anode voltage (a.k.a. maintaining, sustaining, or operating voltage) is given in most, but not all, nixie tube data sheets. However, with only a single rare exception that I'm aware of, all nixie anode voltages fall in a fairly narrow range from about 125 to 155 volts. Aside from tube types, the value also has a lot of variability between individual specimens of any type, and even between cathodes in a single tube. It changes somewhat depending on the current through the tube, and probably drifts quite a bit due to aging effects. When selecting an anode resistor for a type whose maintaining voltage is unknown, most people just pick a starting value based on an arbitrary assumed anode voltage between 130 and 150 volts, and test the actual current to determine whether that initial resistance value needs adjusting.

One advantage to using higher (~200 volts or more) supply voltages, is that tube current will be determined more by the anode resistance and less affected by those other factors. Remember, like LED's, nixie tubes are current-operated and are really not too particular about the volts as long as they get enough to start glowing. Of course, the disadvantage to using higher supply voltage is that there is more power wasted in the anode resistors, meaning more heat produced, and possibly requiring larger resistors and a more robust supply if the supply voltage gets too high. It's all a balancing act between different compromises.

A.J.

-- In NEONIXIE-L@..., "Mike" <mbarile2@...> wrote:

Great little diagram:
Question though, if you are solving for Ra you need to know
this internal Anode Voltage correct? ...
Is there a way to determine this optimal drop and thus
solve for Ra??

It's an iterative process. You make a best guess at the start. The anode voltage (VN), usually ranges between 130V to 150V. Try 140V for starters. Calculate, and insert the tentative RA, in a test setup; Never the final circuit. Measure the VN across the nixie, and WRITE IT DOWN. Now you have your VN, or VA, (VA=VN) as its often called.

Also note, you don't need to be exact. ALL technology, including electronics, never is. Calculate a resistor that will be in the proper operating current range, assuming the voltage is 130V, and then assuming its 150V. If you calculate a value that's good for both, use it.