John Miles wrote: > 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 > John
Perhaps everything is now coated in Caesium, especially the electon multiplier input dynode insulation?? Bruce _______________________________________________ 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.
