David, > I had a similar concern about a brand new 5071a I just purchased,This unit is dated may of 05 and was first powered up Jan 2 of this year..
If it's really been turned off all that time, I'm surprised that it was able to power up. Was the Ion Pump current much higher for some period of time before it came down to 6 uA? How do you know it was manufactures in May 2005? > the ion pump has remained constant at 6 ua This may be as low as it's going to get. You might try putting the 5071A in standby mode for 24 hours or so, to allow just the Ion Pump and not the Cs Oven to operate. It might bring down the internal gassing a bit. But then again that may be as low as you get. It's not abnormal, especially for older CBT, or one that has been allowed to accumulate internal vapor pressure. > but I the electron mult volt has been dropping about 1-2 volts per day > since then.it started out at 1525 and is now at 1297 and still falling This is fine, and well within expected operation. The 5071A automatically adjusts the EMult voltage to maintain the 100 nA beam current. You have plenty of room to drop without concern. The good thing is that the lower you go, the more headroom you'll have when ultimately the beam current begins to weaken and need increasing EMult to maintain. It should eventually flatten out before it starts to rise. If it does get down to 800 to 600 volts without flattening out, then it will very likely have a problem. It may be a symptom of lots of internal gassing that is getting too much background signal to the EMult dynode. No cure for that but to send it in for repair. > all the other parameters are fine but I noticed the osc freq control has > been dropping also it is now at -6.84,started out at -5.50.. This is fine. You don't have to worry until and if it gets to 50% or more. Then it's time to tune it in, which is a bit tricky. Get copies of the O&P and Service manuals from the Symmetricom web site in PDF format and you'll have many of these answers. > do you think these is a problem with this tube?it is a high perf..should still be under warranty as the manual says there is a 5 year warranty on tubes 4240 prefix.. You appear to have purchased a good 5071A. Did you buy it used? One obvious question is: Is it locked? Dave _______________________________________________ ----- Original Message ----- From: "David Welch" <[EMAIL PROTECTED]> To: "Discussion of precise time and frequency measurement" <[email protected]> Sent: Friday, February 08, 2008 9:59 AM Subject: [time-nuts] cs beam tube failure??? Dave, I had a similar concern about a brand new 5071a I just purchased,This unit is dated may of 05 and was first powered up Jan 2 of this year..the ion pump has remained constant at 6 ua but I the electron mult volt has been dropping about 1-2 volts per day since then.it started out at 1525 and is now at 1297 and still falling all the other parameters are fine but I noticed the osc freq control has been dropping also it is now at -6.84,started out at -5.50..do you think these is a problem with this tube?it is a high perf..should still be under warranty as the manual says there is a 5 year warranty on tubes 4240 prefix.. have you ever run into this before?any suggestions..Thanks David _______________________________________________ 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. _______________________________________________ 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.
