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Replace Neon NE-2 with Zener in 141T PSU?
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Ah, but alas, you need the electrons (beta particles), and they
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can't go through the glass. It is probably better to leave the incidental radium sources alone. 1/4 of us non smoking humans are going to die of cancer anyway (1/2 of the smokers), no need to up your odds higher than they already are. -Chuck Harris Artek Manuals manuals@... [hp_agilent_equipment] wrote: Go down to one of those 2nd hand store with your geiger counter and find a very old |
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Oh dear I seem to have started something. The comment about rejuvanating neons was annecdotal refered to VR105 and the kind of neon tubes used a relaxation oscillators.
Now yes I suggested UV, and some glasses do block UVB but to quote Wikipedia (not always a reliable source :-)) Common soda lime glass is partially transparent to UVA but is opaque to shorter wavelengths, whereas fused quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm. Bear in mind for striking you do not necessarily need "free electrons" it may be sufficient that the light reduces the work function of the metal components (or the glass) so electrons can be ripped out by the field. You do not need many electrons to strike the tube. It was offered as a "try it and see" I would be as interested as others to know if it could be useful. Alan G3NYK. |
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Hi,
I had the same problem and replaced the neon reference with zeners. This was after two sets of blown fuses and a post for help on this group.? This was back in 2012.? Then the advice was replace with zeners and a warning that the zeners do not provide the same stability as the neon. I do not remember what zeners I used; there is only the note I put in the manual "2 OCT 12 replaced neon voltage reference with zeners".? I pluralised the zener so more than one. I checked the voltage transients at turn on and was appalled at the high voltage spike; nearly 130 volts across the 82 volt reference.? Those numbers are burnt into my memory but not the number of zeners used! Little wonder the fuses blew. Lesser versions of this event must be occurring in HP 141t analysers across the planet at each turn on. Once the neon started conducting the voltage was both correct and stable. It occurred to me afterward that MAYBE I could have paralleled a slightly higher voltage zener with the tube and had the best of both worlds.? No start up spike and the stability of the neon reference. Did not try so I do not know if it would have worked, perhaps the neon tube would not have struck with the voltage limits imposed by the zeners.? Or the neon would strike but the partly conducting zeners would still introduce noise. My 141t has been working happily with this mod. Cheers Mark VK2WU |
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There are two phenomena going on here.
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The reason that there is a radioisotope inserted into "neon" references, is the neon strikes at a different voltage when exposed to light, vs dark. This is an always thing. The second thing that happens is the neon gas gets buried into the glass envelop by the sputtered electrode material trapping it against the glass envelope. Sputtering changes the composition, and pressure, of the gas mixture, which changes the overall characteristics of the tube. So, if you have a neon voltage *reference*, it will always have some radioactive material sintered into the electrodes to prevent light/dark strike voltage differences. If the neon reference has changed its gas composition too much to strike, for whatever reason, it will have the wrong voltage reference value too... regardless of what you do to make it strike. As to whether adding light of this or that energy will cause the neon reference to strike over, that it happens at all is the result of the photoelectric effect, where stray electrons are created by the glass envelope, and the electrodes, when the photons strike. Ultimately, it is the electrons that reduce the strike-over voltage (see Paschen's law for more info). -Chuck Harris David Wise david_wise@... [hp_agilent_equipment] wrote: Would you guys slow down long enough for me to type a reply? :) |
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Most of the trouble in the PSU pcb seems to stem from overheating, due to the fact that there`s very little moving air. I used a chassis punch to make a couple of holes in the bulkheads downstream of the fan to help with this. Cheers!......Don Collie ZL4GX On Sun, Jul 16, 2017 at 1:08 AM, Chuck Harris cfharris@... [hp_agilent_equipment] <hp_agilent_equipment@...> wrote:
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