[time-nuts] Fwd: FE-5680A Physics package

J. L. Trantham jltran at att.net
Mon Oct 31 08:05:44 EDT 2011


Somewhere, I have read an article about 'resurrecting' a 'dead' Rb bulb.  I
think it was done with heating but I do not recall.  I probably have the
article squirreled away somewhere and I can probably chase it down if
someone else on the list does not come up with the link first.

Are you familiar with what I am talking about?


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Peter Bell
Sent: Monday, October 31, 2011 1:00 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Fwd: FE-5680A Physics package

Following up on my own post - it seems it is the Rb cell that's the problem
- I swapped the cell over (it's just held in place by hot
glue) and fault moved with the one from the bad unit. After removing the
heat-shrink, there are two separate glass cells in the assembly, as I
suspected.  The smaller one (on the left in the photo) was the one closest
to the lamp and if it contains anything at all, it's not visible.  The
second, slightly larger, cell seems to be the actual absorption element and
contains a small quantity of some silvery metal (I.E. Rb)  partly in the
pinch and partly deposited on the glass.

It all looks so simple it's hard to see what the problem could be - the only
thing I can think of is that the first cell has leaked (the second one
obviously hasn't, since the Rb is not oxidized).  The other conclusion that
I've reached from this is that these units are pretty non-critical - as long
as I used the good Rb cell assembly, it would lock with any combination of
housing / heater / photocell, RF multiplier assembly and C-field coil /
shield.  Ah well - put it to one side until / if I get another dead unit, I


On Sun, Oct 30, 2011 at 3:31 AM, paul swed <paulswedb at gmail.com> wrote:
> My comments have been about other rb cels and the fact that components 
> in the rf oscillator tend to die and are generally replaceable. 
> Additionally using the practice of heating the emission cell with heat 
> gun to re-evaporate the accumulated rb seems to really revive a cel. 
> So if its dead what the heck have some fun. I wrote up my info and its 
> on Diddiers and Stanleys sites. Others like Magnu's and Stanley have 
> written up their tricks. So good luck.
> Regards
> Paul.
> On Sat, Oct 29, 2011 at 12:54 PM, Peter Bell <bell.peter at gmail.com> 
> wrote:
>> I was wondering if anyone on the list has ever had a play with these 
>> things?  I had a couple of dead ones, and have managed to get the 
>> first one working (easy fix - the 3.3V regulator was dead), but the 
>> second seems to be a lot more troublesome.
>> Basically, everything seems to be working, but there is no resonance 
>> dip detected at the photocell - however all the individual parts seem 
>> to be OK.  I did a couple of quick and dirty tests firstly by 
>> swapping the entire Rb cell assembly over between the two units - and 
>> the fault swapped over with the Rb cell.  Both cells are running at 
>> the same temperature, the photcells are good, and the working one 
>> still works (on both main boards) even when you swap the snap diode / 
>> filter assembly or the shield / c-field coil from the bad one.
>> Basically, all that's left is the photocell (which seems to pick up 
>> light OK), the FET / Thermistor (unlikely, since the heater works 
>> correctly), the lens (looks perfect) and the Rb cell itself.  So I'm 
>> tending towards the "bad Rb cell" idea - but the problem is that I've 
>> fixed quite a few Rb oscillators in the past (mostly Efratom FRKs and 
>> a few FRSes) and I've never seen a bad Rb cell.  So I was wondering 
>> if anyone else on this list thought it seemed likely.
>> (resent with the photo reduced in size).
>> Incidentally, when I was looking at the Rb cell, I noticed that it 
>> seemed to be a pair of cells held together in a heat-shrink tube - I 
>> assume that the first (slightly smaller) one is a isotopic filter and 
>> the second is the actual absorption cell?
>> And does anyone have any schematics for these things?  FEI seem to 
>> have the standard "send it back to us" approach that is increasingly 
>> common recently - another reason I liked the FRSes.
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