[time-nuts] HP 5065A rubidium lifetime

[Bob Camp]

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