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: [email protected] [mailto:[email protected]] 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: [email protected] [mailto:[email protected]] >> 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: [email protected] >>>> [mailto:[email protected]]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 >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
