Is your oven doing what it is supposed to be doing? Sounds more like an oven problem than a crystal problem.
--- Graham == On Sun, Nov 20, 2016 at 7:00 PM, Alan Melia <[email protected]> wrote: > Michael a couple of wild thoughts, make sure there is no 500kHz there > (this is the crystal fundamental and the maintaining circuit should be > degenerative there. (Is it a Meecham Bridge?) > > That sounds like a baseless IO GT valve (tube in US ) enclosure which was > probably originally evacuated....has the vacuum gone soft in 50 years?....I > dont know how you would check, but I think that would cause a lowering of > the frequency. > > Alan > G3NYK > > ----- Original Message ----- From: "Michael Ulbrich" <[email protected]> > To: "Time-Nuts" <[email protected]> > Sent: Sunday, November 20, 2016 11:49 PM > Subject: [time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad? > > > > Hi there, >> >> I'm new to this list and have some interest in quartz crystal and >> rubidium oscillators - GPS, NTP, PPS and "clock watching" in general ;-) >> >> I snatched an R&S XSD frequency standard accompanied by an XKE frequency >> controller. Found the manuals on KO4BB's site (Thanks a lot for that! >> BTW there's a slight mix-up of pages in that some of the XKE pages have >> found their way into the XSD manual). >> >> My initial hope of a quick and easy restoration project faded a bit when >> I looked at the XSD output frequency after heating up the oven. It was >> off by about -1 * 10-5 and after cranking the fine tuning for some time >> and having another look at the specs I realized that the frequency was >> too far off to be dialed in by the fine tuning which only covers about >> +/- 2 * 10-7. >> >> Next step was to take apart the oven and check series capacitor, >> oscillator and the crystal itself. I found that even the coarse >> adjustment range of the cylindrical series capacitor (40 - 110 pF) would >> not allow to pull the crystal to it's specified frequency. When >> replacing the series cap by a ceramic and lowering the value to just >> before the oscillation breaks down (about 10 pF) I managed to set the >> oscillator frequency offset to +2.5 * 10-6 at room temperature. But >> even this will not suffice when taking into account that the frequency >> will drop by a few parts in 10-5 (cf. XSD manual) when the oven heats up >> to its operating temperature. I also checked some of the components on >> the oscillator PCB which might have an influence on frequency but could >> not find any fault. >> >> The crystal itself is a disk of about 30 mm diameter mounted in a sealed >> glass cylinder of about 38 mm dia. and 43 mm height. There is no socket >> just 2 bare wires.. It does not show any visual signs of damage. >> According to a reference given in the R&S XSD manual the crystal's >> construction follows a publication from A.W. Warner "Design and >> Performance of Ultraprecise 2.5-mc Quartz Crystal Units" in Vol 39, >> Issue 5 of Bell Labs Technical Journal (Sept. 1960). According to that >> it is an AT-cut 5th overtone design. >> >> Now my questions: >> >> a) Considering that this gear is about 50 years old, a "crystal gone >> bad" situation shouldn't be that much of a surprise, right? But could >> there be any other cause of the "huge" frequency offset besides a bad >> crystal? I would very much appreciate any idea that I could try to get >> this baby back on spec. >> >> b) if nothing else helps: Could any of you give me a hint about who >> might be able to supply a spare crystal? I tried my directly reachable >> contacts but unfortunately to no avail so far. Please consider that >> similar crystals might also have found their way into other >> manufacturer's constructions from that era - Sulzer, Racal, HP ... you >> name it ... >> >> Many thanks in advance! >> >> Best regards ... Michael U. >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/m >> ailman/listinfo/time-nuts >> and follow the instructions there. >> > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
