Count me in on learning the ways of HP DMMs and from Chuck no less.
Paul
WB8TSL

?? There is a collection of all issues of the Boonton Experimenter.

Thanks for the info George.  I was pretty sure
your warning was aimed at high impedance sources.

I await your video lectures with bated breath.

-Chuck Harris

ghnatiuk@... wrote:
Hello,
Regarding connecting high quality voltmeters in parallel.  It depends on the resolution the meter is capable of and the impedance of the voltage source.   An instrument such as the 3458A has an A/D that is capable of 100 million counts or 0.01 ppm an 8 digit DMM).  Meters of  5 and 6 digits will not in general be affected.
...
I started to make a series of videos on the design of high quality lab grade multimeters detailing what I learned while designing these DMM front ends at Hewlett Packard.  Unfortunqately, I never finished them and did not publish the series.  I will get busy over Christmas and finish the videos on how I designed the front ends of the Hp3468A/78A series of meters.  Those designs are also used in the 3457A and 3458A meters and everything I discuss regarding the 3468/78 is also applicable to those meters as well.  I indended the videos to be very detailed so that other engineers can use my experience to leverage off and get up to speed quickly without having to spend years as I did experimenting and testing designs and learing through the school of hard knocks how to protect the sensitive front ends from abuse and reducing leakages and other sources of error.  The videos discuss each passive and active component in the front end and the reason they are there and the reason they have the values they do.   Stay tuned.  I will post the video links here when I finish the videos.

Thanks
George Hnatiuk  Dec 11, 2019  12:19am
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There are manuals, yourtubes, and many other resources available on these lovely test instruments.? I have two of them that work perfectly.
Make sure the power supply is doing its job.? Those use a constant voltage transformer arrangement that can cause trouble when its buried-in-tar capacitors fail.? It took me a long time to get all the tar off my body when I repaired one.
Otherwise it appears you are on the right track.? Generally, exercising the turret will bring all positions back to life. Check the tube sockets as well.? Measure tube voltages and compare to what should be.
Once you get it working you will have a fine addition to the workbench, albeit a large one.? Since acquiring a nanoVNA I have found very little use for the Boonton, as the nano can do it all, perhaps witl a bit less precision.
The frequency accuracy and stability are excellent.? Just be careful to heed the warnings regarding the fragility of certain components.? Basically it puts a current through an inductor, which it resonates with a calibrated capacitor and the rise in voltage indicates the Q.? The capacitor calibration indicates the inductance.? For measuring capacitors you add the unknown part and see how much you need to reduce the calibrated dial to recover resonance.? To measure resistors you see how much they degrade the Q.? And so on.
Seldom are troubles due to failed tubes, although it happens. See that the filter capacitors in the poewr supply are doing the job, as well as the aforermentioned constant voltage transformer.
Bob K6DDX
On Wednesday, December 11, 2019, 04:12:48 AM PST, Steve Hendrix <stevehx@...> wrote:
Thanks to all who responded with lots of good information. I was able to get to my parents' yesterday with time to actually work on the thing together. It appears that the unit is overall functional, but that amazing carousel that switches in the components for the oscillator to do different frequency ranges has some problems, most likely the contacts. I am in awe of the mechanical engineering that went into this thing, in the days when vacuum tubes were expensive - today a 20c IC has way more active elements than this whole instrument.
I tried cleaning the round rods on the carousel that engage the fixed contacts, using a sponge saturated with contact cleaner and passing the sponge between the rods so as to clean the area that makes contact with the fixed contacts. I made no attempt to reach the fixed contacts directly, as that would require some major disassembly (or much smaller fingers than mine or Dad's!). I was hoping the residual contact cleaner on the moving contacts would clean any residue off those. The unit is overall really clean inside, and the flat metal fixed tabs appear to be in good shape and properly tensioned, although maybe could use a bit more tension.
I took the following data, using the numbers handwritten on the carousel that seem to correspond to the range numbering in the service manual. This suggests that there's no overall major problem, but that some of the sections aren't making contact (or have a problem within the section, as a less likely possibility). The sine waves all look very pure, and indeed the FFT feature on my scope didn't show any objectionable distortion. Measurements were taken by unplugging P201, and cobbling up a connection to that BNC.
Range ???????? Behavior across tuning range
1 ???????? Fixed at 306 KHz, 1Vpeak
2 ???????? Dead
3 ???????? 287KHz 1Vpeak to 725KHz 2Vpeak
4 ???????? Dead
5 ???????? 1.38MHz 15Vpeak to 3.5MHz 25Vpeak
6 ???????? 3.5MHz 10Vpeak to 9.2MHz 22Vpeak
7 ???????? Dead
8 ???????? 19.3MHz 26Vpeak to 40MHz 1Vpeak
So, can those here with much more knowledge of these things, please guide me on where to go next? I really hesitate to just go poking around in this, or especially to unnecessarily disassemble anything, because I'm well aware that these older instruments sometimes had some very clever engineering that required specific mechanical spacings, etc. I don't want to destroy an irreplaceable instrument.
Steve Hendrix
At 2019-11-29 12:56 PM, Bob Albert via Groups.Io wrote:

On 11/29/2019 6:00 AM, Steve Hendrix wrote:

At my parents' home yesterday for Thanksgiving, my dad showed me
a Booton Type 260-A Q Meter. He is a long-retired EE, and this
instrument was given to him by a friend of similar age, who
inherited it from his own father. Based on the styling, the use
of vacuum tubes ("valves" to our Limey friends!), and the use of
"cycles" for what we today would call "Hertz", I'd guess it

dates

from the 40's or 50's. Dad thinks it's non-working, but we

didn't

want to take too much time away from our family gathering, so
just turned it on. The power light illuminates, and all the

tubes

appear to have good filaments. I have found and downloaded the
user manual and service manual, and it appears to have been

taken

over by HP at some point. Next visit I plan to take my scope
along and I look forward to diving into it together. Meantime,
does anyone here have any knowledge of this critter, any tips,
etc? Although I'm one of the "young whippersnappers" of this
group, I'm old enough to know about tubes and HV capacitors and
to keep one hand in my pocket, etc. Although it's billed as a Q
Meter, it appears to have much more capability, pretty much what
we call an LCR meter today, covering "50 KC to 50 MC".

On 11/29/2019 6:00 AM, Steve Hendrix wrote:
> At my parents' home yesterday for Thanksgiving, my dad showed me
> a Booton Type 260-A Q Meter. He is a long-retired EE, and this
> instrument was given to him by a friend of similar age, who
> inherited it from his own father. Based on the styling, the use
> of vacuum tubes ("valves" to our Limey friends!), and the use of
> "cycles" for what we today would call "Hertz", I'd guess it dates
> from the 40's or 50's. Dad thinks it's non-working, but we didn't
> want to take too much time away from our family gathering, so
> just turned it on. The power light illuminates, and all the tubes
> appear to have good filaments. I have found and downloaded the
> user manual and service manual, and it appears to have been taken
> over by HP at some point. Next visit I plan to take my scope
> along and I look forward to diving into it together. Meantime,
> does anyone here have any knowledge of this critter, any tips,
> etc? Although I'm one of the "young whippersnappers" of this
> group, I'm old enough to know about tubes and HV capacitors and
> to keep one hand in my pocket, etc. Although it's billed as a Q
> Meter, it appears to have much more capability, pretty much what
> we call an LCR meter today, covering "50 KC to 50 MC".