[time-nuts] cs beam tube failure???

[David Welch]

I opened the box for the first time,,the unit was new and still in the vac
bag..the ion current started out and has remained at .6ua..always locks in
about 15-18-min..one other unit he had for sale that the seller had opened
and had running had a (for two days)had a emult of 1715 and also .6 ua
current..when I got there to pick up my unit his emult had also dropped from
1715 to 1700 in 24 hrs time..

one note when I power down or put my unit into standby the pump current will
go down to .4 and even .2 but not for long ,,,after running for several days
it usually goes back up to .6..I just had it in standby last night for a few
minutes and it is still at .4 ua today.but now shows 1295 emult volts...

the unit locked for its first time after 2+ years in storage in 21
minutes...the calibration certificate shows a manuf date of may 11,2005..but
when I called them they said these were no longer under factory warranty
because agilent only offered a 3 yr warranty..and this was one of the very
last agilent units made..
----- Original Message ----- 
From: "Dave Carlson" <dgcarlson at sbcglobal.net>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Saturday, February 09, 2008 1:47 AM
Subject: Re: [time-nuts] cs beam tube failure???


> 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" <aceamusements at mchsi.com>
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> 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
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