I recently found a tube from a 5062C on eBay in unknown condition for not *too* much money, and thought it would be interesting to power it up on the bench. Once I got it and saw the 19xx-prefix serial number, I wasn't too optimistic, since it could potentially be 25 years old or more. Things went well for the first few steps of the process, but then the experiment failed big-time.
1) I first applied +2600V to the ion pump with nothing else connected. Spec is < 10 uA. There was a brief spike to ~100 uA, but within a few seconds, the current began to drop rapidly, ending up at about 1 uA after a few minutes. So far, so good. 2) I then brought the Cs oven up to temperature slowly with a variable supply. The 5062C runs its oven in a thermostatic loop, but it was easy enough to warm the oven up slowly over 10 minutes or so, watching the thermistor resistance to achieve the 200-ohm reading indicated on the tube label. The ion pump current rose to about 2.5 uA during the Cs oven warmup process. 3) I then attempted to bring up the hot-wire ionizer, which takes 1 volt at about 1.6 amps (when hot). Simultaneously, the 22-mA C-field current and 13.9-volt mass-spec supply was applied. As with the Cs oven, I brought the ionizer voltage up slowly. 4) At that point the ion pump supply went into full current limiting at circa 300 uA. I killed the power quickly, removed the oven and hot-wire ionizer supplies, and tried powering the ion pump up by itself once again. Although a DMM check indicated infinite resistance across the ion pump, the HV supply still went into current limiting. I'm guessing that the hot-wire ionizer element had enough crud on it to kill the vacuum when it vaporized. The tube envelope is probably OK, because the ionizer wire itself didn't burn out. Unfortunately I was watching only the hot-wire ionizer current during that part of the process, so I don't know if there was a point where I could have observed a rise in ion pump current and backed off in time to avoid permanent damage. The last step would have been to connect the -1900V electron multiplier supply, feed in a 9.192632 GHz signal from an HP 8672A which would be frequency-modulated with a slow sawtooth, and watch for an output signal on a scope with a high-Z opamp buffer. Unless there is some kind of sequencing taboo that says "bring up the electron multiplier before the ionizer", I don't immediately see what I might have done wrong. Anyone see any obvious newbie mistakes in the account above? Or was it just a matter of expecting too much from a Cs tube that might have been 20 years old? For what it's worth, the electron multiplier also shorts out its (negative) supply now. I don't know if that would've happened earlier, since I never tried to energize it during the pre-test checkout. -- john, KE5FX _______________________________________________ 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.
