I think teletekj...@gmail.com has some that were removed from working unit to upgrade to the more stable board.
On Wed, Jan 28, 2015 at 7:07 PM, Randy Evans <randyevans2...@gmail.com> wrote: > I bought two HP-3458A ref boards from John Daly (he no longer has any more) > and they worked fine but have intermittent noise bursts. I suspect they > were rejects from HP/Agilent. At some point I will probably replace the > LTZ1000As and reduce the internal temperature set point for better > stability. Has anyone else had any issues with these units? > > BTW, I packaged the units in an enclosure for a stand-alone reference and, > except for the occasional noise bursts, seem very stable according to my HP > 3458A and fluke 732A/ESI RV722 KVD. > > Randy > > On Wed, Jan 28, 2015 at 9:40 AM, John Phillips <john.philli...@gmail.com> > wrote: > > > There is a bottom cover under the board. > > > > On Tue, Jan 27, 2015 at 9:01 PM, J. L. Trantham <jlt...@att.net> wrote: > > > > > When these boards are installed in a 3458A, the LTZ1000 is covered by a > > > small, white, 'hat' that mounts with screws that pass through the two > > holes > > > on opposite sides of the LTZ1000. I've never removed the board to see > if > > > there is anything on the bottom of the board that would cover the > bottom > > of > > > the LTZ1000. > > > > > > Does anyone know what this 'hat' is constructed of or the > > > HP/Agilent/Keysight part number of this item is? Is it available from > > > Keysight? > > > > > > In the 3458A the reference board is under a cover that covers about > half > > > of the top of the meter but not 'insulated' beyond that, except for the > > > 'hat' referred to above. > > > > > > It would appear desirable to find what that 'hat' is and see if > something > > > could be fabricated to 'insulate' the LTZ1000 for a 'do it yourself' > > > standalone reference. > > > > > > Would appreciate hearing anything about how the reference board is > > > 'insulated' in the 3458A. > > > > > > Thanks. > > > > > > Joe > > > > > > > > > -----Original Message----- > > > From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Orin > > Eman > > > Sent: Tuesday, January 27, 2015 11:45 AM > > > To: Discussion of precise voltage measurement > > > Subject: [Bulk] Re: [volt-nuts] 3458A reference boards on ebay > > > > > > Dave, > > > > > > I'll be putting it in an enclosure to use as a reference. It will > > > probably be a smallish diecast aluminium box. It's what I did with my > > > Geller SVR-T and it compared very well with my Fluke 731B. I'll likely > > use > > > Pomona 3770 binding posts for output (I used them to repair the 731B). > > > I'll also use the protection circuits from the Fluke 732 on the output > - > > > big reverse diode, gas discharge tube and TVS as I recall (I plan to > add > > > these protection circuits to the 731B). > > > > > > I'll likely do a PCB for it, though the local equivalent of veroboard > > > would likely be OK; the socket spacing is 0.9" and the pin spacing > 0.1". > > > My meters are also 6 1/2 digit (3456A and 34461A) so I'm not too > > concerned > > > with thermal EMFs with one count being 10uV on the 10V range. > However, I > > > will try to avoid temperature gradients and keep the outputs close > > > together. I'll use star wiring for the 18V and ground as in the > > following: > > > > > > http://www.maxmcarter.com/vref/ > > > > > > It is debatable whether the -15V supply is needed - I'll test with and > > > without. I'd add a few tantalum capacitors to the above design - on > the > > > regulator outputs and on the 3320 resistor, along with protection > diodes > > > for the LM317. > > > > > > There is also a HUGE thread about the LTZ1000 on EEVBlog - I'll be > > > reviewing that for ideas: > > > > > > > http://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/ > > > > > > I actually have a couple of LTZ1000As here that I was going to DIY, but > > > never got around to getting the precision resisters . I think there > is a > > > source in England mentioned in the EEVBlog thread. > > > > > > Orin. > > > > > > On Tue, Jan 27, 2015 at 2:24 AM, Dr. David Kirkby (Kirkby Microwave > Ltd) > > < > > > drkir...@kirkbymicrowave.co.uk> wrote: > > > > > > > On 27 January 2015 at 09:16, Orin Eman <orin.e...@gmail.com> wrote: > > > > > There is a seller letting a slow trickle of them out there... they > > > > > seem > > > > to > > > > > be going for about $165. The current batch of two is around $100, > > > > > but > > > > will > > > > > probably be bid up. > > > > > > > > > > I just received one that I won. Seems to be working fine after a > > > > > quick breadboard lashup. I'll be making an enclosure for it next. > > > > > > > > > > A little expensive IMO, but given the trouble getting the precision > > > > > resistors to DIY with the LTZ1000A, probably worth it. > > > > > > > > > > Orin > > > > > > > > Orin, > > > > > > > > What do you intend doing with it? > > > > > > > > I was thinking about getting one of those, with a view to putting it > > > > in a box with a couple of terminals to have something to compare with > > > > my 6.5 digit 3457A. But what put me off is a lack of knowledge in > > > > knowing how to convert a 3458A reference board into a boxed unit with > > > > a known output voltage at the terminals. How would I avoid / control > > > > thermal EMFs? > > > > > > > > I'd be interested to hear what your plans are for it, and how you > > > > intend tackling those issues. > > > > > > > > Do you know what the difference in the reference is between a > standard > > > > 3458A (8 ppm) and the high stability option 002 (4 ppm) model? I'm > > > > guessing the chips for the option 002 might be the top performing > > > > ones. I wonder if there's any way to tell from your board if it came > > > > from a standard 3458A or a 3458A with option 002. > > > > > > > > Dave > > > > _______________________________________________ > > > > volt-nuts mailing list -- volt-nuts@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@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@febo.com > > > To unsubscribe, go to > > > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > > and follow the instructions there. > > > > > > > > > > > -- > > > > *John Phillips* > > _______________________________________________ > > volt-nuts mailing list -- volt-nuts@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@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > -- *John Phillips* _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.