[time-nuts] HP 5065A rubidium lifetime

[J. L. Trantham]

Thanks.

That is just the type of information I was looking for.  

I have some pictures of my 'melted' unit with the covers off the end of the
cell end if anyone is interested.  It is pretty messy after the meltdown.
There are at least three metal cylinders for sure, an outer one then foam
between it and the next one, then foam between the second and third one then
foam inside that between the inner cylinder and the aluminum cylinder that
is the rubidium lamp assembly. 

When I started trying to disassemble the unit, I could not get the aluminum
cover of the lamp assembly to turn loose.  I replaced the three 2-56 screws
that hold the cover in place with longer ones then used a 1/2 inch thick
aluminum disc with a center hole placed over the center bolt of the lamp
assembly, resting on the long screws.  I used one of the nuts and 'torqued'
it to 'pull' the cover off the lamp assembly cylinder but to no avail.
However, after the melt down, with everything 'hot', it came off relatively
easily.  This is what makes me think it had had a prior 'meltdown' and the
'goo' had dried as an incredibly strong glue.

Although mine was destroyed, it did not appear to have a 'twisted pair' type
winding but rather a single layer.  I had missed that it was a 'parallel
pair'.

Thanks,

Joe



-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Chuck Harris
Sent: Saturday, March 20, 2010 11:38 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] HP 5065A rubidium lifetime


Hi Joe,

The original winding was wound with parallel (non twisted) bifilar wires.
The two wires at the entrance to the winding went to the oven circuitry, the
two wires at the exit to the winding were shorted, thus forming the
"hairpin".  There were hundreds of turns of wire tightly wound in a single
layer.  I recall that the wire was about #36 AWG.

I replaced the winding with some coaxial heating wire that I found
someplace.  It has been something like 25 years since I did this.

As I recall, HP wound some Kapton tape on the aluminum oven assembly, and
then wound the nichrome wire over the tape.  The whole assembly fit loosely
in the mumetal can that encloses the entire physics package. They expanded
some kind of foam in the space between the assembly

I knew the oven was shorted, and I had little to lose, so I just pressed the
assembly out of the can.  This exposed the oven winding.

When I foamed the oven, I used a couple of wooden wedges to hold the
aluminum oven centered in the shield.

I seem to recall that there were two mumetal cans, with foam between them.
One had a tuning solenoid winding, and the other had a heater winding.

All of this is pretty foggy...

-Chuck Harris