Things to be careful about! "I think the final vacuum improvement can be achieved more quickly if the cesium oven is on."
The outgassing in a tube that has been off for an extended time is almost all from the oven filaments and the ionizer filament. The metal surfaces are virtual "sponges" and getter any gases that are available. If you turn them on with no protective cycling circuit you run the risk of overloading the ion pump to the point where it cannot pump at all! Don't use the 200Meg divider voltage to determine the output voltage of the supply. Unloaded it is a correct representation of the output voltage. (4Vdc equals 4000V out)However any appreciable load causes a counter voltage that drops the divider voltage a lot! The divider voltage might then read 1 volt but the output voltage is still over 3000V. (it's designed that way to shut off the ovens if the divider voltage drops.)Use a Fluke 80K-40 divider probe or similar on the output as it has a very high input impedance. A recent measurement of 4 A18 supplies shows an output voltage of 3000 V with a 50ua load. Also if testing the supply on the bench you must ground the case of the supply to the minus input pin. If you don't your HV will read half of what it should be. Ion pump supplies for vacuum maintenance like for Cesium tubes, Hydrogen Masers, and some high power Rf TX tubes are just for that, "maintenance". This allows low power consumption, small footprint, and long life. On the EFOS Maser here the ion pump supply has a max rating of 2ma, this for a large 20 liter pump. If you are running a tube at high ion pump currents you might have 20na of beam current but check the peak to valley ratio. Just because you can get to 20 na does not mean the tube is performing well. Running an Allan Deviation plot is the easiest way to know for sure. The oven filaments are very robust, the ionizer filament due to the required shape is not. If you are using the older A11 module then the ionizer voltage is AC and causes vibration of the filament which can result in premature failure. Once HP came out with the new A11 (DC on the filament) they would not honor a tubes warranty if you were using the old style A11. Cheers, Corby Dawson _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
