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

Dave Carlson dgcarlson at sbcglobal.net
Sat Feb 9 02:47:42 EST 2008


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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