Marvin Posted >... for short term stability as transfer references, no time statement what short means, I presume at minimum the time it takes to receive US mail from coast to coast The length of what a Short term Time means is all relative to how long it takes to do the Transfer test. >From several seconds under ideal conditions to days If it is being shipped across the USA. Several minutes would be a more typical case. To do the TC test of the attached plot showing the "Zero TC" using one of Geller's Modified AD587 Reference boards, Short term stability was over a 24 hr period. Time to let the Temperature change slowly AND more important is to check it on the way back for repeatability. The thing that seems to be skipped over a bit too lightly is to get the Best reference for a Volt Nut, (or freq nut) no mater what you're using, It is ALL about aging, grading and selecting the best from a bunch of them and then making the best better, by matching or TCing or whatever. What Geller's stuff did was allow me a Fast, Cheap, and Easy way to sort thorough a lot of stuff to make several and find the best ones. WarrenS *************************** [volt-nuts] Best reference after LTZ1000 Marv Gozum @ JHN marvin.gozum at jefferson.edu Tue Aug 24 17:37:12 UTC 2010 Previous message: [volt-nuts] Best reference after LTZ1000 Next message: [volt-nuts] Best reference after LTZ1000 Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] Hello Charles, Thanks for the links and the insight. Sorry for delay, but was also reviewing the old commentary on time-nuts about the Geller references, his patents, and more on voltage standards not on this lists' archives. Overall though, the more important item is taken as a whole is this box with the patented stabilizing circuit a better reference than something else, assuming this is what your friend has? I agree with your criticism of the circuit function. See the schematic on the patent. There is a novel item, notice that the supply voltage for the LM399 comes from the vref output of the AD587 op amp, rather than V+ as expected? This provides an ultra stable supply for the LM399, compared to one from a standard regulator or battery, while also putting a continuous load on the op amp. Not sure what this does to the ppm/oC over time, so I would think Geller should characterize such as effect better to capitalize on it. Geller does offer the patented circuit on a stabler and more costly version of SVR, but you have to ask him for it. Its near $300 compared to the $35 SVR. But I think there are more conventional ways to achieve stability without the uncertainty of this circuit's function. If others aren't aware, the Time Nuts archives around 2008/9 have discussions about WarrenS's modification and his experience with Geller boards and chips, mailed to-fro East and West coast USA, and his experience with its stability. There are other posts affirming Geller and Malone's boards at least for short term stability as transfer references, no time statement what short means, I presume at minimum the time it takes to receive US mail from coast to coast. Thanks a bunch again, for the leads and comments.