[volt-nuts] Serious problems fluke 731A, 720 and solartron

[Fred Schneider]

Hi David,
I have the original manual that came with the 731A when bought from Fluke in 1974. Inluing notes, mods ect.

The 720 Kelvin Varley is OK again, another centre isolator was cracked. I made a new one from teflon, cleaned the other switch and it is now good again. Lineair in all ranges, nice instrument

I sounds like I only have trouble but that is not true, because I have some good calibrators (332, allways giving same results in relation to the guildline, philips DC calibrator , idem, and a fluke 760) and a guildline 4 cell with full history. 

I know calibration figures upto 1988 and measured them using a brand new Keithley 2000. If I take a big safety margin and extrapolate the numbers i know the value within 15 uV worst case. But the best cell dropped 50 nV a year, the worst 499 nV. The measurements with the keitley gave a inter-relation still the same as back then but then calculated on the level it must be now. The first 5 year they "settled" and after that the graphs went lineair so I calculated where they must be now and meaured them and the difference was 15 uV but the chance the 2000 is 15 uV off, is bigger then the Weston cells worn more then calculate because they were stored very carefull ( just stayed in the rack all those years it was put in when they bought it new, but never used or calibrated it, before 1988 it was calibrated every year from 1974 when produced) the oven is on the temperature it alway was.

That is why I know for sure the solartron and the 731A are not good, the 731 is not important, i made two Vrfs that are on 24/7 and they are pretty stable by now, ( 1,000.000V and 2,500.000V ) the other calibrators too. But I just like to have the 731A good also. Just for fun.  It was not working when i got it. There were notes about a repair and one of he note was: need to order a new reference zener. But i do not know how good the tech at the company was, the 845 was also declared dead by him, but the repair was simple ( all gear was donated to me , fully documentated, by company that closed its cal lab) the Fluke 8500 was also written off, but I got that working again also.

Just wonder how I find out if its the Vref or the ompamp that does behave strange. I do not know if a zener reference can get "half defect" and the opamp takes over its function as good as it can. If that is possible then its the zener ( is the transistor  in the reference is germanium it can be something like whiskers)

The 845AB is very good, i know for sure, i compared it to several other meters. Made some modifications to get it maximum stable.

Fred


>> 
> 
> Fred, you can buy a manual for your Fluke 731A from https://www.ridgeequipment.com/store/manuals/detail.php?id=12771.
> 
> From your description of all of your problems, I think it's time for some outside assistance.  You need to get one or more of your instruments checked out and repaired by someone who has the necessary equipment to verify operation.  You don't have any equipment that is in known good condition. Are you confident that the null meter is working properly?
> I think I would start with the Fluke 332 and the 731A voltage standards. Once you know that they are working properly and calibrated, you can then use them to verify your 729 divider and null meter.
> 
> David
> dgminala at mediacombb dot net
> 
> 
> 
> 
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