Poke it with a laser with more ability to aim the beam on or around the two posts.

Thanks for sharing this !

Strange that this video just came out while I was watching a video about using neon lamps as memory.

Wow. You revisited this and did not read up about these neon bulbs. Oh well, no commenter caught on either. I suppose there are no old physics teachers watching. I pointed out in previous series how the metal coating on electrodes have a low work function which helps the emission process. Flickering is a sign that coating is becoming degraded.

A 405 nm blue/violet laser pointer works really well for this... A NE-77 trigger tube with its three electrodes would let you tease apart what it actually going on, as will DC biasing. It is fun to sweep the bias too, an old curve tracer makes this easy but a mains transformer (especially a vacuum tube supply transformer or a pair of filament transformers to make an isolated ~150 volt AC source) and a few resistors works to make one.

@IMSAIGuy

3 жыл бұрын

Never seen a NE-77 they look really interesting.

Imagine that! Enjoyed!

I know about this effect, I’ve seen neons buried deep inside equipment before and knew they used this effect for something, but had forgotten the details 👍🏻 Glad you did this tho 😉

Yes, Mr Carlson is rebuilding an HP 410 which is an AC VTVM and differs from my HP 412A, a DC VTVM. in several regards. Carlson's instrument has a valve mounted in an AC probe. His instrument and mine were manufactured over the same time frame, 55- 70- or so. I was astounded to see that HP charged $250 for the 410 when Palo Alto began the run. A guy on EEVblog asked if the 410 was supposed to be the holy grail because they command a lot of dinero today. I also discovered that some of the 412A units used incandescent bulbs in the chopper. Mine are neon or my cataracts are worse than I thought. Same guy reported that the photocell in the chopper needs to be exposed to light at all times ??? My 412A came out of a lab at Oregon State U per the ID tag. It's in great shape, cosmetically, but has something like a 4 mfd filter cap, I probably should change out. The one thing I really like about the 412 over the 410 is that the 412 has a mirrored meter which is larger than the non- mirrored 410. That's all I know.

Probably photoelectric effect dampened by the dilute gas. Natural to have an asymmetry in charge flow with asymmetric illumination. You could try putting a small bias on the bulb, with illumination from one side and see if you can get the photoelectric current curves. I remember watching a video which used the neon bulb as a (very inefficient) Geiger tube.

@jspencerg

Жыл бұрын

The visible light has enough energy to overcome the work function of the electrodes' coating. You created a net current by asymmetrically lighting which asymmetrically produces photoelectrons. A wonderful ammeter you have! You might be able to determine actual work function energy by using tungsten light source incrementally heated up. Photoelectrons escape(producing measurable current) when their kinetic energy (equals hν) >metals work function. Would need a spectrometer to get highest frequency of light being emitted just when a current starts to flow.

I think you are ionizing the electrons of the cathode or anode metals. These metals have work function, which is photon energy needed to ionize the metal electrons. When you shine mostly on anode metal you ionize anode's electrons and anode becomes positively charged. When you shine mostly on cathode's metal, cathode's metal electrons ionizes and leave the cathode positively charged. You can reduce the work function of the metal by heating it up, as it is done by filament in vacuum tube .

Per HP manual, these neon bulbs are part of the mod/demod circuit. Some are on a "light bar." Need to read more on this.

Thanks for the interesting video! In out collection we have a bunch of Elektronika D3-28 (Электроника Д3-28) machines, the Soviet computers loosely based on Wang 700 series of calculators. They have 7-segment nixie displays which for some reason cannot quickly light up on power-up after the machine was turned off for a quite long period of time. A flashlight or just turning on lights in the room usually act like a trigger making the display lit. Looks like it needs some amount of ions to ignite the initial discharge and than the process continues on its own. More interesting that the display in D3-28 is not static, it works in dynamic manner with 1/16 duty cycle (2 rows of 16 digits) and has a pretty high update frequency. I still don't know exactly if the effect is due to gas itself or it's somehow connected with other parts of display (electrodes, glass, getter, whatever).

You made me run out to the shop to look at my HP 412A VTVM , which has a neon array which glows so brightly that the light streaming through the louvers casts shadows. Now I'll have to read up on this....

@IMSAIGuy

3 жыл бұрын

That does not use photoelectric effect. It is just an old school optocoupler used as a chopper stabilized amplifier. Also interesting

Perhaps the bulb causes some refraction. Do you have a UV light laying around? Not sure if the difference in wavelength is significant enough to be measurable.

How about an ordinary tungsten bulb? Would that produce a measurable current?

time to see if it can work as a solar tracker

Thanks. It looks like the chopper is an electromechanical mechanism. When it eventually dies, it dies, my 1958 manual directs the user to contact the HP rep for replacement. Fortunately, mine is still working.

@IMSAIGuy

3 жыл бұрын

I remember someone rebuilding it. Mr Carlson?

Do you get the same positive/negative effect when the neon bulb leads are switched, or is it always one electode is pos and the other neg ?. Also, try it with a Nixie. Cool stuff for the clever folk to work out. :)

@electronicengineer

3 жыл бұрын

This is a great question and I also wonder if the polarity follows a specific lead/terminal or what. What is going on here?

@_lwza_

3 жыл бұрын

@@electronicengineer Could be wrong, but I vaguely remember reading that some of these bulbs have one electrode doped with a radioactive material like Thorium that lowers the ionisation potential. Could this explain the effect?

Weird. I've just to try it myself :)

why do u think vacuum spark gaps have a radioactive dot...?

@IMSAIGuy

3 жыл бұрын

didn't know they did. pre-ionization to control breakdown?

Try to break one light bulb to let the gas out and see if that still works the same way?

@IMSAIGuy

3 жыл бұрын

nope

Strange as you would think the two electrodes are identical and the gas is the gas so how does it know which electrode is being illuminated? Maybe the two electrodes are not the same? Any neon bulb engineers left out there?

@absurdengineering

2 жыл бұрын

The electrodes are coated and they are never the same in spite of the best efforts to the contrary. As far as I can tell, the slight dissimilarity (including the slight asymmetry of mounting) is enough to produce a measurable effect. On some bulbs, the sensitivity goes through the roof if you polarize them well - say 5mA DC for 5 minutes. It doesn’t always work though - no idea why, yet. It’s also worth looking at how they behave after running them in arc discharge for, say, a second.

Try the test using a broken neon bulb, to see what effect the neon gas has.

@IMSAIGuy

3 жыл бұрын

nothing happens

zeroth

I am thoroughly confused as to how a glass gas discharge tube envelope (filled with neon gas) and two (2) parallel tungsten electrodes (neon lamp with approx. a 90 volt breakdown voltage) can possibly emit a polarized current, just by exposing it to white LED light. How does one of the electrodes distinguish itself with a reverse polarity from the other electrode, when both are exposed to the same light, at the same time? I realize that there is usually a small amount of radioactive material added to neon lamps, to improve ionization in low light conditions, however, how can one of the electrodes choose a polarity over the other one, with just neon gas in the envelope? I really don't get it... Fred

@absurdengineering

2 жыл бұрын

The electrodes are somewhat dissimilar. Anything with emissive coating is different from everything else with such coating, and usually the difference is greater the more you actually want them to be the same :) Neon bulbs polarize very quickly at DC, with one electrode gaining in emissivity while the other loses it. Neons are definitely not in a perfect “identical electrodes” state - neither when new nor when running with AC.