https://www.febo.com/pipermail/time-nuts/2017-March/104374.html
You bring up an interesting point. As the cesium is used up over the years, it forms a cesium frost which deposits on everything inside the tube. If it gets thick enough it conducts or can arc between frost grains. A charged capacitor can blow some of this away. Cesium melts at 83° F. If you heated the beam tube up in a hot car or out in the hot sun, you could turn this frost into dew. The dew might run down hill into some cesium lakes where it was harmless. Those lakes would freeze when back at room temperature and might be even more harmless. I have seen two TV picture tubes that developed leakage between focus and screen electrodes. Adjusting focus changed the brightness and adjusting the screen changed the focus. I applied the high voltage between the two and the arc burnt out the high resistance leak. It saved both picture tubes. WB0KVV πθ°μΩω±√·Γλ ======== If you cannot get the ion current below 50ua or so after a week at 5kV then you are out of luck. Most likely you have resistive deposits on the ion pump insulator. If you can get the tube to give a decent SN at those levels then you can run with the alarm circuit bypassed. I have run tubes a couple years this way (at <50ua) but if you let them sit cold you will have to manually cycle the ovens at turn on until the excess gas load is pumped. If you have a bad ion pump supply when you open it up to repair it I would suggest adding a 66K resistor across the 75K resistor. This will increase the alarm trip up to about 40-45ua. If it's the older one the oil capacitors will need changing as well as the 200Meg resistor. If the later one (in the 5061B) then the 47uf radial cap is open. both these units are interchangeable. One other trick is to use a spark discharge tester (miniature hand held tesla coil used in the neon sign industry) to ZAP the ion pump lead. This can blow out any whiskers that the ion pump has developed. You can also (carefully) with the HV on, remove and replace the ion pump connector a few times. Sometimes you will get a sharp discharge that blows out the whisker. I have used both methods with good success. Cheers, Corby _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.