What will happen if current slightly below specification in long time?

[overdoingism Lab.]

My nixie clock has a switch, with three level, full - low - off.

The low level setting does make the tube look a bit dimmer.

And the current seems to be slightly below specification.

For all I know, it's probably not good for "Cathode Poison", but I can switch back to full level to flush them.

Besides, is there any disadvantage?

BTW, Is there any way to adjust the brightness? PWM doesn't seem like a good idea.

[Christian Riise Wagner]

Out of curiosity, why doesn't PWM sound like a good idea? There isn't really an alternative, other than lowering the current, which you don't seem too fond of either. I'd say PWM is the easier method. Just choose a sufficiently high frequency to avoid noticeable flickering. Note that the ammeter averages out readings, so whether the tube is driven at a constant reduced current or PWM, the reading will be lower, even though PWM is full current delivered in pulses.

[gregebert]

I've seen a few postings about audible noise coming from tubes that use PWM.

I use direct-drive and constant-current.

[Nicholas Stock]

I've made a number of Tubehobby's IN14 clock kits over the years as gifts for friends and family. They're multiplexed IN14 clocks. No audible problem and the clocks are still working well after 12 years. The only complaint is those damn IN3's and their tendency to ionize all over the place! 

Nothing wrong with multiplexing IMHO.

Nick

Sent from my iPhone

On Jan 14, 2023, at 09:19, gregebert <greg...@hotmail.com> wrote:

I've seen a few postings about audible noise coming from tubes that use PWM.

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[overdoingism Lab.]

For the following reasons:

1. High voltage swing PWM, I am afraid it will cause EMI interference.

2. As far as I know, the impedance has a sharp change during the lighting moment. (As arc discharge?)
PWM driving may mean more heat generation, more aging and wear? I'm not sure.

3. If you want to completely avoid audible noise, the PWM frequency should be raised above 30khz. (Not only tube, also coil.)
Considering that is voltage >150v , the stray capacitance effect will become significant, and there may be reliability and safety hazards.
And also, I'm not sure Nixie tubes are responsive enough.

About these reasons.  (I'm not sure if my concerns are correct.)

Christian Riise Wagner 在 2023年1月15日 星期日凌晨12:53:18 [UTC+8] 的信中寫道：

[Christian Riise Wagner]

The voltage across the tube starts high, while the tube impedance is high, before the gas discharge has been established. The current then rises relatively slowly, while the voltage drops at a proportional rate due to the anode resistor. Threeneuron has an excellent page on driving nixies, which also has a scope capture of a Nixie striking. The lack of surge current should mean that there won't be additional power dissipation and thus heating during this period. Also, because the current doesn't rise that fast, that should limit the high frequency components of EMI emissions.

In regards to audible noise, I think this depends on the physical construction of the tubes in use. I don't have a large sample size in this regards, as I have only implemented dimming and cross-fading on my Z566M clocks and haven't noticed audible noise from that. I'm running it at 400Hz IIRC. 

I guess a valid point could be that if the tubes are generating audible noise, that could mean that there are some physical stresses being being exerted, which could cause wear. The glass to metal joints are the weakest spots. This is pure speculation though, and I think there are multiplexed clocks out there that have been running for a couple of decades on end by now.

[overdoingism Lab.]

Thanks for the information, they are very helpful. :)

Christian Riise Wagner 在 2023年1月15日 星期日下午5:45:03 [UTC+8] 的信中寫道：

[jf03...@gmail.com]

This may not apply to other tube types, but my 3 clocks built with 6 x  B7971s were MUXd at about 2 kHz, and they all produced enough acoustic noise to be annoying in a quiet room, and RFI audible over the entire AM band that was detectable on my transistor radio to about 20 feet.  The clock was enclosed on all 6 sides in a box made of 1/4" plexiglas, and the electronics (except the tubes) were in an aluminum chassis.  Someone once suggested that the noise came from the switching power supply, but I used a linear supply with old-fashioned 60-Hz power transformers and the noise changed whenever the characters in the display changed.  BTW, 45+ years without any tube failures.