8/10/2023 0 Comments Neon cathode![]() ![]() This radar had "op amps" which were 4 tubes but worked just like any op amp today. I stumbled across a now forgotten art about 30yr ago in what was then a then old radar that used neon tubes (~1cm diam 2cm long) internally as voltage references, used rather like zenner diodes (current sources). leakage and impurities, as thermal expansion and contraction will open ways for molecules to get out of or in to the tube's envelope. ![]() This last point is exactly what I would have suspected to be the secondary failure mechanism, i.e. as well as design) are not to be regarded as reliably hermetically sealed. 4.) that the envelopes, which feed a metal wire through glass without special considerations (Kovar etc. 3) that SOME sputtering (during production?) is beneficient due to a getter effect, which binds non-noble gas molecules. the second phase is characterized by sputtered deposits trapping additional gas molecules when forming the abovementioned deposit. The first phase of this is happening, when ions encounter surface defects on the anode and/or the envelope. He names the 'cleanout'-effect, which he describes as being both physical and (to a lesser degree) chemical in nature, which causes the density of the gas filling to diminish. 2.) cathode sputtering is the prevalent, but not the only effect which is determinating the lifetime. Mulder in his book 'Gas Discharge Tubes' (1963) states, that : 1.) cathode sputtering is dependent on current and gas presure, with higher pressure reducing the sputtering. The reason is that if the current is too low to keep the complete electrode area involved in the discharge, the non-emitting spots will passivate over time and not enter emission even if the current is increased again. It is also noted that a lower-than-intended cathode current should be avoided too when the electrodes are oxide coated. Further he states that the end of the lifetime of any glow-discharge devices is characterized by steadily raising ignition and maintaining voltages, with erratic changes also occuring. He also states that it is cathode sputtering which is causing the dark deposit. O.P.Herrnkind in 'Glimmroehren und Kaltkathoden-Relaisroehren' states that electrode sputtering 'Elektrodenzerstaeubung' is a certain factor, which is proportional to the operating current. Behind this is the bigger value and factor of influence of the limiting resistor on the operating current, which is very small when 110V and coated cathodes are involved. (Open, short, and anything related to filaments.) All sources give higher lifetime for 220V indicator neons than for 110V types. The are semingly thrown together with the incandescent annunciator lamps, which makes the data not applicable. Unfortunately, the RAC Failure Mode Distributions do not show any separate data for glow lamps. ![]()
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