[time-nuts] cesium clocks..

wje wje at quackers.net
Sat Jun 28 14:49:59 EDT 2008

   The heater winding for my 5061A crystal oven doesn't seem to be bifilar
   wound, but it's a little difficult to tell. Since the heater works, I
   don't want to risk poking around too much. However, one lead comes in
   at one end, the other lead is at the other end.
   BTW, my oven failed again, this time because I was lazy the first time
   I fixed it. There was a fairly crispy resistor I didn't have a
   replacement for. It seemed OK, so I left it in place. Of course, it
   just failed. I had to open everything up again and replace it. While I
   was in there, just to make everyone happy, I rerouted the power and
   heater return lines that I had moved outside the foam back inside,
   replacing them with some nice, Teflon-insulated, fine-gauge wire I had.
Bill Ezell
They said 'Windows or better'
so I used Linux.

   Chuck Harris wrote:

Bruce Griffiths wrote:

Chuck Harris wrote:

This is a chicken vs egg sort of problem.  When I took apart the oven
on my 5065A rubidium, it looked to me as though the enamel insulated
nichrome wire developed a short about 50% into the coil, and wiped out
the transistor.  It also heated the rubidium lamp hot enough to reflow
the solder on its circuit board and thoroughly char the PCB's epoxy.

I am not sure how the quartz ovens are wound (I suspect they are the
same), but with the rubidium ovens, the nichrome wire is wound as a
bifilar loop.   This is done for two reasons, 1) to cancel the magnetic
fields, and 2) to make the start and finish wires of the winding happen
at the end of the oven where the terminals are.

-Chuck Harris

An Ayrton-Perry style winding will also have low magnetic field.

There are no doubt hundreds of ways of achieving the same result,
but HP used a single layer bifilar winding of enameled nichrome wire
that was shorted on the far end.

When I replaced the oven winding on my Rubidium, I used a shielded coaxial
winding that was also shorted on the far end.

-Chuck Harris

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