John, What you describe with the ion pump curent is normal if the tube has been powerd off for a long time. Th mainframe normally would turn the oven and ionizer filaments off when the ion pump current pegged. After minutes (can be quite a few minutes) the ion pump current will drop as it pumps the surge of outgassing from the heated filaments. The cycle repeats and can take a couple days on a stubborn tube. You bypassed that circuit so I'm not sure how much gas you introduced. If after a couple days the current is still pegged try connecting an external high voltage supply of around +3000VDC that can provide at least 5ma. (turn unit off) Let it run overnight and if the current comes down reconnect the internal power supply and turn the mainframe back on. You probably will see it peg again and the see the oven shut down (it happens fast!), just leave it on and it should start cycling and eventually the filaments will reach the oven set points and have outgassed enough so that the protective circuit will not trip. Then you can try to see if the rest of the tube has any life. (you may have to reduce the oven set resistor to 130 ohms as well as reducing its companion overtemp resistor. This is the value the Navy uses to get the last bit of life out of the tube, don't do it if you can get the rated beam current at the original value!) If you email me I can give you my evening phone number if you need some more info. Corby Dawson cdelect@juno.com ____________________________________________________________ Click here to find the perfect picture with our powerful photo search features. http://thirdpartyoffers.juno.com/TGL2141/fc/PnY6rw1aBm8XXBA9eC72NBG9alhmVMe3ZD9uri8B4mlt3xxDXctvb/

Hmm! I appreciate the tip. I'll confess it didn't occur to me to try to force more current through the ion pump. The supply I was using was limited to about 300 uA, but I took your advice and tried a beefier one, set to 3 kV. As I increased the current limit from 0 towards 5 mA, the ion-pump current fell back to ~25 uA once I reached 1000 uA. At the rate I was adjusting the current-limit control on the Glassman supply, this occured about 10 seconds after power-up. It seems stable now at 25 uA, several minutes later. I didn't leave the hot-wire ionizer energized for more than 10-15 seconds, all told. I'll let the ion pump run for a few hours, and then try the hot-wire ionizer again. Should I bother with the other supplies (Cs oven heater, EM, mass spec), or is it reasonable to recondition the tube using only the ion pump and hot-wire ionizer terminals? Keep in mind that I don't have a 5062C mainframe, just the Cs tube and some bench supplies. I'm essentially recreating Tom's experiment from http://www.leapsecond.com/pages/cspeak/ but without benefit of an actual clock mainframe. So I don't have a filament shutdown/recycle controller in the picture. Obviously that would be needed if I were to actually build a clock around the tube, but for now, I just want to see if the tube is functional at all, and determine its figure of merit. -- john, KE5FX > John, > > What you describe with the ion pump curent is normal if the tube has been > powerd off for a long time. > > Th mainframe normally would turn the oven and ionizer filaments off when > the ion pump current pegged. > > After minutes (can be quite a few minutes) the ion pump current will drop > as it pumps the surge of outgassing from the heated filaments. > > The cycle repeats and can take a couple days on a stubborn tube. > > You bypassed that circuit so I'm not sure how much gas you introduced. > > If after a couple days the current is still pegged try connecting an > external high voltage supply of around +3000VDC that can provide at least > 5ma. (turn unit off) > > Let it run overnight and if the current comes down reconnect the internal > power supply and turn the mainframe back on. > > You probably will see it peg again and the see the oven shut down (it > happens fast!), just leave it on and it should start cycling and > eventually the filaments will reach the oven set points and have > outgassed enough so that the protective circuit will not trip. > > Then you can try to see if the rest of the tube has any life. (you may > have to reduce the oven set resistor to 130 ohms as well as reducing its > companion overtemp resistor. This is the value the Navy uses to get the > last bit of life out of the tube, don't do it if you can get the rated > beam current at the original value!) > > If you email me I can give you my evening phone number if you need some > more info. >