[volt-nuts] introduction

Tue Apr 26 22:18:22 UTC 2011

I think I have the manuals complete, they are original and I do not miss
pages but maybe there is also a real extended service manual for the
845AB. 
In my schematic there is a A and a AB powersupply schematic. The A has a
zener and no battery. They removed the battery in mine, that was also
written on the cabinet and placed two zeners. I think they did not get
it right anymore and then bought the Fluke 8500 that was part of the
setup (in the drawings I had in the documentation it was coupled to the
750)

Tonight I did some first measurement. The Cells are now about a month or
two operational and heated. They are very carefull moved to a special
made shelf two weeks ago. But now I have a problem. It's like the man
with just 1 clock, he think he does know the time, the man with two
clocks has a problem. I have 4 DC calibrators and 4 Weston cells so I'm
lost :-)  

I first measured 1 cell from the Guildline using the 845 and the 731. I
turned the 731 dial until I had a zero in the 3uV range and allmost zero
in the 1uV range. I took that value as a reference. Following the trend
in the graphs from this cell (from 1977 upto 1987) the value could be
realistic. The oven temp is 30.07 degrees. The philips was about plus
250uV, the 332 was minus 160uV. But if I connect them through the 750 I
get a 25uV difference. I have not tried to calibrate it, it is always
kept in the same clean room and never messed around so it will be
probably better if I leave it like this because the 720 is not usefull
and needed for calibration.

The 720 is strange, it is clean as a baby inside-out. It is not been
dropped or so. But all the plastic is cracked and broken. If you touch
it it crumbles. Maybe someone back then cleaned it with some solvent.
It's a pitty because it is a beautifull instrument. I must find some
teflon or poly-ethilene to make new ones (I have a lath and a mill but
is is a lot of work) Some are possible repairable using 2K-epoxy. One
switch, number 1 from right, is very bad, I had to take it out because
the centre-follower is crumbled. The others still work and are in place
but the studs have cracks and pieces allready missing.

73

Fred  

WB6BNQ schreef op di 26-04-2011 om 13:20 [-0700]:
> Hi Fred,
> 
> Looks like you got lucky with such a nice collection being offered.
> 
> I am confused on why additional zeners would be added to the 731 and 845.  Both
> were made to work without batteries.
> 
> The 731, if it is in good shape, is an extremely stable reference source.  Well
> able to transfer a known value from a competent calibration Lab to use for
> establishing the value of your Guildline cells.
> 
> As I am sure you know, the 845 is the only high impedance DC NULL meter available
> that was worth a damn.  The first mains power transformer (and battery with its
> charge circuit) is just to supply a power source for the 84 hertz transistor
> inverter to the neon's.  That same inverter is also used to power the all of the
> circuitry.  That is part of what provided the extremely high input isolation.
> The noise you see on the 1 uv scale is normal.
> 
> The 720 switch problem sounds interesting, I wonder what caused the switches to
> be so bad ?  In a clean environment there should be no reason for them to have
> disintegrated.
> 
> The Guildline was a very nice catch.  Have you had an opportunity to determine if
> the cells are in good shape ?  Hopefully nobody loaded them with a low
> resistance, that would have messed them up for sure.  In conjunction with the
> 845, 750 and the 731 you have yourself a nice voltage reference system.
> 
> As for cables, well, I would not worry about that.  Just use normal copper wire
> and you will not go wrong.
> 
> From your comments I am wondering if you have the full manuals for the 731 and
> 845 ?
> 
> 73....Bill....WB6BNQ
> 
> 
> Fred wrote:
> 
> > Hello,
> >
> > My name is fred, PA4TIM, I'm a volt-nut. Took a lot of therapy to
> > confess ;-)
> >
> > I was already fascinated by calibrations because I restore measurement
> > equipment. I collected some old calibrators like an old one from Philips
> > using nixies as indicator, a Tek AC calibrator ment for internal factory
> > use.
> >
> > But a few months ago a got a mail from a stranger who noticed my website
> > and asked if I was interested in the stuff from his companies old
> > calibrating lab (for free !!!) The lab was closed 25 years ago, but the
> > stuff stayed there unused. Now they needed the room and "found" this
> > stuff but almost nobody knew what it was so a lot was thrown away. He
> > thought that was a shame and asked if he was allowed to find a
> > collector. Al stuff including manuals and calibration history and in
> > state like new. But not used for 25 years and some stuff suffered from
> > sleeping or was maybe already death when parked away
> >
> > It started with a Guildline 4 cell unit. In perefect condition. I had to
> > repair the heater and some minor aging things.
> >
> > A tek 576 curve tracer came as a bonus with a box new Tek parts.
> >
> > Then things speed up, if I wanted some more. A complete Fluke
> > calibration setup. To bad they tossed away all cables.
> > -332B voltage standard, worked like a charm after changing one cap.
> > -760A meter calibrator, worked for a week, now constant jumps in
> > protecting and the home fuse blowes even if I put the plug in powered of
> > so I think a Y capacitor is leak. I will find that, no problem (I hope)
> > -510A AC reference standard, dead batteries but I just removed them
> > because they are optional. I left in the option board. Still not sure if
> > that is wise.
> > - 731A, also dead nicads. I removed them and put in a 12V voltage
> > regulator. Also had to replace a paper-foil capacitor.
> > - 750A voltage divider. There is room for two strange batteries but as
> > far as I understand it also workes without as long as you are sure You
> > do not over voltage
> > -some HP stuff like a 20 penta Ohm elctro Ohmmeter/voltage source, a
> > time standard, pindiode modulator and low distrotion sinewave generator.
> >
> > But then two very important parts of the set up. A 720 kelvin Varley
> > divider. All see-through plastic isolator standoffs and centre coupling
> > parts of the switches are desintegrated. That will become a hell of a
> > job.
> >
> > The biggest problem was my 845AB, they allready removed the nicads and
> > added two extra 10V zeners. Thick metal multi-amp ones.  The problem is
> > the manual is very limited. There are some scope pictures and a small
> > trouble seek section.
> > I had to replace allmost every cap, so did them all. Then I kept
> > problems with stability. Then I took my lab-supply and put 10V over the
> > capacitor. It drew about 30mA and was stable. Then I raised the voltage
> > and when the zener started conducting the 845 draw 600mA. I think the
> > 10V mega-zeners started drawing so much current the transformer
> > saturated or at least power got unstable. Could not close the top lid,
> > as soon as it came near the transformer the meter went nuts. I now
> > placed a 7812 and it is stable over the whole range I think. At 1uV full
> > scale with shorted input and knob at zero the meter deviated plus/minus
> > 0,1 uV max, most times about 0,05uV. I think that is not bad but this is
> > my only null-detector so I do not know for sure.
> >
> > Now I have to find out how to make cables to connect everything, find a
> > way to determine what will be my  STANDARD VOLT. I have the calibrating
> > history upto 1988. I can measure the differences between the cells but
> > first have to find out the safest way, and if that is comform the old
> > papers I think I take that as a basis. Then adjust the calibrators to
> > that value. This will probably still be more accurate as the average
> > multi or bench meter. I have a 6,5 digit as best one.
> >
> > Does some one has a better way ?
> >
> >
> > For my collection See www.pa4tim.nl Not all the fluke stuff is on it
> > yet.
> >
> > 73
> >
> > Fred
> >
> > _______________________________________________
> > volt-nuts mailing list -- volt-nuts at febo.com
> > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
> > and follow the instructions there.
> 
> 
> _______________________________________________
> volt-nuts mailing list -- volt-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
> and follow the instructions there.