I would like to share with you my thoughts on two important points that concern a little all attempts to modify and upgrade the equipment.
In general I am very reluctant to modify both the electrically and mechanically, in this case, the HP5065A. Modifying, even completely a board, I agree if there is a significant improvement, trying to use the existing pinout and, in the need for additional connection points, use additional connectors on the board. As regards the space on the pcb, smd components can be used whenever possible or doughter boards. Remove boards, transformers or anything else I find reluctant, I would prefer to have the possibility of being able to go back to the original configuration if necessary. The area occupied by the optional batteries, which I think almost nobody uses, can be used for new electronics. Using a switching power supply with better performance I agree and since there is already a dedicated DC input on the back of the 5065A I would prefer to use the one to connect to an external box that contains the new power supply and the management of a backup DC input. This eliminates the need to dismantle anything inside the HP5065A. Another important point is that of the certainty of the results of a change. I mean that most hobbyists who have a 5065A, including me, do not have the opportunity to measure the proposed improvement effects, first of all because they do not have a reference such as an HMaser available, nor even such a refined measuring system to appreciate the improvements made. I want to remember that between zero and 8kseconds the GPS system (e.g. HP GPSDO) in our laboratories has an Adev higher than that of the HP5065A and therefore the measure we do in that range is that of GPS, not that of rubidium. For this reason I invite all those who dedicate themselves to these very interesting changes proposed to test the results obtained in depth and to share them with us with numerical and graphic elements. I take this opportunity to thank them in advance for their scientific help. I want to specify that this is my point of view, it is not a rule and not necessarily shared by other people. thankyou , Luciano Luciano P. S. Paramithiotti tim...@timeok.it www.timeok.it Da "time-nuts" time-nuts-boun...@lists.febo.com A "Discussion of precise time and frequency measurement" time-nuts@lists.febo.com Cc Data Tue, 4 Aug 2020 13:32:31 -0400 Oggetto Re: [time-nuts] "The Penultimate HP5065 A15" Hi If a more extensive rebuild is in the works ….. +/-20V is (as has been observed) not an ideal voltage for “modern” electronics. If you dig into each of the boards, there is a lot of “drop it down right now” regulation done on a board by board basis. More or less what might be there: A1 Synth A2 Battery Charger A3 60 MHz multiplier A4 100 KHz divider A5 Digital Divider (= clock) A6 1 MHz divider A7 AC amplifier A8 Phase detector A9 Integrator A10 OCXO A11 Rb temp control A12 Rb assembly A13 5 MHz buffer A14 Logic A15 Power supply A16 Power for clock A17 Terminal board A18 Jumpers ( = alt for A2) A19 Led Clock board For most uses, A4,A5,A6,A16,and A19 are not required. A2 is just a pair of diodes (A18) rather than a battery charger. A17 is more part of the wiring harness than anything else. Looking at what’s left: A1 synth, this seems to be a target for various replacement schemes. Right now, it has a bunch of positive voltage rails with some circuits running on 20V. Replacement likely would run on <= +12. A3 Multiplier. Again a target for replacement in some schemes. Same supply as A1 for replacement. Existing design runs +20 direct to a lot of circuits. A7 AC amplifier. Now runs +/-20V. Pretty much begs for a modern op-amp based replacement board. +/-12 probably is fine for that board. A *good* -15 would work for the existing board with minor mods. A8 Phase detector. Replacement probably is all digital. Now runs +20V A9 Later version of the board runs +/-15. Probably would work fine a good +/-12 with minor mods A10 If it’s a 10811, it’s going to need > +18 for the heater and +12 for the OCXO. There are other “at least as good” parts that work fine on +12. A11 Unless you want to redo the heater windings on A12, you are stuck with +20 to +30V. Rest of the board sort of begs for a modern op-amp approach. A12 Lamp assembly is the only load (other than heater windings and C field). It does run on +20V. A13 +20V taken to +9 for everything on the board. Simple mod to run on +12 (or +15 or +10 …). Replacement likely runs on +12 A14 If the upstream boards get changed, this likely does as well. Sort of begs for a $1 MCU and a handful of resistors as a replacement. A15 ( the topic of discussion) So, there are two “customers” for -20V. Both would be happy with a fairly good -15V instead. If the replacement OCXO for A10 tunes 0 to 5V, the need for a negative supply becomes a bit unclear. There are a couple of places you can’t easily get around 20 to 30V. The heater windings on the physics package are the biggie. The Rb lamp driver is probably not worth messing with. If you keep A1, A3, A7, or A8, they will need the existing +20V. +12 or +15 makes more sense for their replacements. A13 could easily be modified and run on +12 or +15. ==== So why all this long winded yack? The ultimate need for +20 is really pretty small. The lamp still needs it. The heaters need something in that vicinity. They don’t need the super regulation or low noise that the lamp needs. The -20 probably does at least as well as a -15 V supply, even as the device sits right now. Long term -15 makes more sense. A bulk +12 (and maybe +5) likely take up the heavy lifting for most of the boards once they are modified. Indeed they would be useful even on the existing boards. Does this change anything you do on the A15 right now? Maybe not. It is worth thinking a bit on though. Bob > On Aug 4, 2020, at 6:35 AM, Poul-Henning Kamp <p...@phk.freebsd.dk> wrote: > > -------- > Magnus Danielson writes: > >> If that is the range you aim to improve, then I strongly recommend you >> do re-read the postings I did about phase noise in detector range, as I >> have showed that phase-noise get's mixed down to DC and increase the >> noise there. With very ugly and hand-wavey hack I was able to >> significantly reduce that noise essentially by cleaning up the >> phase-noise. > > Ohh, absolutely. > > My plan is to put a modulated DDS synth in to get a much more modern > detector system. > > But right now the zener on my a15 is better at measuring temperature > than holding voltage stable, so I'm addressing that first. > > See the 3rd graph here: > > http://phk.freebsd.dk/hacks/HP5065A/20150908_a15/ > >>>> I would go for the LTZ1000 if you can. The LM399 has gone out of >>>> fashion for a reason: [...] >>> Yes, I know, being also a volt-nut :-) >> >> I have not yet jumped down that rabbit-hole as I am by far not done with >> the current one. :) >> >> I've been looking at the LTZ1000 and one day I may get some. > > You *really* want the version of it which is packaged in the attractive > and *incredibly* useful "HP3458A" cabinet :-) > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
