[time-nuts] HP 5065A rubidium lifetime

[paul swed]

Great thread.
Though no one answered a question I had.
Would it be smart to add a safety. This sounds like a royal pain to rewind a
heater.
I also did not realize you could open the whole assembly up.
Not that I want to. But when the day comes with nothing to loose in I will
go.

On Sat, Mar 20, 2010 at 10:15 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> You make a tightly twisted pair. The ides is to get the magnetic field to
> cancel out.
>
> Bob
>
>
> On Mar 20, 2010, at 9:14 PM, J. L. Trantham wrote:
>
> > Do you make a 'twisted pair' and then wind that or just wind two parallel
> > wires around the cylinder?
> >
> > Joe
> >
> > -----Original Message-----
> > From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> > Behalf Of Bob Camp
> > Sent: Saturday, March 20, 2010 7:59 PM
> > To: Discussion of precise time and frequency measurement
> > Subject: Re: [time-nuts] HP 5065A rubidium lifetime
> >
> >
> > Hi
> >
> > I think I can answer part of that, though I've never dissected a 5065.
> >
> > To make the heater work right you need the proper resistance / foot
> heater
> > wire. Cupron is a pretty typical material if you want to solder to it.
> > Nicrome is fine if you are welding to it.  THe real trick here is to find
> > somebody with a spool of the right stuff and then beg a few feet from
> them.
> >
> > Doing a hairpin and then twisting is much harder to do right than winding
> it
> > tightly and then shorting the end of the pair.
> >
> > The easy way to make the twisted pair is to use an electric drill. Once
> you
> > wind the stuff, both ends are scrap, but the part in the middle is quite
> > good. You loose an inch on each end and get a few feet (or how ever much)
> > out of the middle.
> >
> > Since the maximum temperature the oven can go over ambient rises as the
> > heater resistance goes down (good old P = E^2/R) you might put a heater
> on
> > thats a slight bit higher in resistance than the original. that would be
> a
> > problem when it gets to 0 (or -20) in you basement, but it would take the
> > load off of the rest of the parts.
> >
> > Bob
> >
> >
> > On Mar 20, 2010, at 8:30 PM, J. L. Trantham wrote:
> >
> >> Chuck,
> >>
> >> Can you provide any other information about this repair?
> >>
> >> How much disassembly of the RVFR, what kind of prep of the lamp
> >> casing, how much wire, where did you find the wire, did you 'bend' the
> >> wire into a 'hairpin' or did you wind two wires then short one end and
> >> feed the power from the other end, what kind of prep for the outside
> >> cylinder, what kind of 'jig' to hold everything in place while
> >> applying the urethane foam, etc., etc.
> >>
> >> I have two of these and one arrived dead after which I 'killed' it
> >> some more with a total melt down.  If this should arise again, a
> >> repair guide might be very helpful.
> >>
> >> 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 7:35 AM
> >> To: Discussion of precise time and frequency measurement
> >> Subject: Re: [time-nuts] HP 5065A rubidium lifetime
> >>
> >>
> >> I can't say for certain.
> >>
> >> The heating element is a single layer of formvar coated nichrome
> >> wire.... about #36 gage.  To avoid magnetic fields, they wound it
> >> bifilar, and shorted the far end of the bifilar wires... forming a
> >> "hairpin" loop.
> >>
> >> I found a short about 1 inch into the 5 inch winding, and the oven
> >> driver transistor was open circuited.  The 1 inch that wasn't shorted
> >> was surrounding the area of the lamp assembly.
> >>
> >> I recall that the oven fuse was ok.
> >>
> >> -Chuck Harris
> >>
> >> John Miles wrote:
> >>> What was the root cause of the oven failure in your case?
> >>>
> >>> -- john, KE5FX
> >>>
> >>>> -----Original Message-----
> >>>> From: time-nuts-bounces at febo.com
> >>>> [mailto:time-nuts-bounces at febo.com]On
> >>>> Behalf Of Chuck Harris
> >>>> Sent: Friday, March 19, 2010 9:58 PM
> >>>> To: Discussion of precise time and frequency measurement
> >>>> Subject: Re: [time-nuts] HP 5065A rubidium lifetime
> >>>>
> >>>>
> >>>> When my 5065A had its oven failure, it got so hot that it melted all
> >>>> of the solder joints on the lamp board.  I resoldered the joints,
> >>>> rewound the oven
> >>>> winding, and foamed the unit with some spray can urethane (Great
> >>>> Stuff), and
> >>>> had it working again for a couple of years.  Then something else
> failed.
> >>>>
> >>>> I'd sure like to fix it, but Scott McGrath, representing himself as
> >>>> an employee of Harvard University, borrowed my manual more than a
> >>>> year ago, and refuses to return it.  Oh well!
> >>>>
> >>>> -Chuck Harris
> >>
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> >
> >
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