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.. ----- Original Message ----- From: "Dave Carlson" <[EMAIL PROTECTED]> To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Sent: Monday, February 04, 2008 9:18 AM Subject: Re: [time-nuts] CBT EOL
> Hello, > > Speaking not from a physicist perspective, but from being in the business > for over 20 years... > > The mechanism depends somewhat on the amount of flux that has been traveling > through the CBT, which determines if the cesium becomes exhausted before the > electron multiplier first dynoe "wears out". > > In general with the HP/Agilent/Symmetricom CBT there is enough getter > material inside to trap contaminants well beyond the time that the cesium > should run out in the oven. As long as the Ion Pump is working, internal > contamination should be the minimal contributor to EOL. > > Whether the cesium runs out or the Electron Multiplier first dynode loses > its coating is largely dependent on the amount of flux. The High-Performance > CBT run at a hotter oven temperature to gain better S/N and thereby exhaust > the available cesium at a faster rate. In these CBT the EOL mechanism is > more likely due to that. As the cesium runs out the S/N degrades. Increasing > the EM voltage can help, but eventually you're amplifying more and more > noise. > > In the standard-performance or long-life CBT the EOL mechanism is more > likely due to the first dynode of the EM becoming depleted of its coating, > than buildup of internal contaminants. > > Dave > > ----- Original Message ----- > From: <[EMAIL PROTECTED]> > To: <time-nuts@febo.com> > Sent: Monday, February 04, 2008 6:39 AM > Subject: [time-nuts] CBT EOL > > > When a CBT reaches end-of-life, is it because the source of Cs is used > up? Or is it due to contamination of the electron multiplier? > > I've heard both as causes but wanted more info. > > I have a CBT with very low beam current and it keeps falling. I'm wondering > if running a higher than normal EM voltage might help keep it on > life-support. > > -Brain, WA1ZMS/4 > > _______________________________________________ > 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. > > > _______________________________________________ > 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. _______________________________________________ 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.
