Hi Judging from your data, the pot takes the oven from at or above the inflection temperature of the crystal down to a point well below the crystal’s lower turn temperature. That’s about all it needs to do.
Bob > On Mar 11, 2016, at 11:19 PM, [email protected] wrote: > >> Hi > >> Anything electrical (duty cycle/ harmonics / output level / etc) >> is designed in on a modern part done in high volume. > >> The only candidates for a pot on top of the oven are: > >> Inner oven temperature >> Outer oven temperature >> EFC > >> You have already ruled out EFC (it would be a coarse set so >> visible on a normal counter). > >> That leaves inner oven and outer oven. > >> Why inner oven - to adjust for the data from your temperature run. The parts >> are at best coarse set based on crystal temperature. > >> Why outer oven - same as above or to set for inner / outer separation >> and clearance after the thermal stabilization in the sealed can. > >> If there is no apparent change in frequency (and from the location of >> the pot) that suggests the outer oven. Regardless of which oven is being >> set, the >> adjustment is likely a “move it 1.25 turns" sort of thing. You then >> re-run the temperature test to see if it is in spec yet. > >> Bob > > > Bob, > > In a separate communication, Angus has stated... > >> On the two that I tested, it appeared to adjust the temperature of >> both of the ovens. > >> One was a 5 MHz 260-0545-B. The outer oven was at 78.2 degC and at >> least around that point the temp changed at about 1 degC per turn. The >> EFC adjustment on this one was not quite enough to bring the frequency >> to exactly 5 MHz, but the oven temp did look to be close to correct. > >> The other was a 16.384 MHz 260-0546-G which was unused old stock, but >> had overall poor stability. It turned out that the oven temp on it was >> 1-3/8 turns from the turnover point, but when or how that happened I >> don't know. > >> It would be interesting to hear from somebody who knows how this type >> of thing is actually adjusted in production. > > I finally got my 260 (sort of) repaired and have done some measurements. > > Generally, I can confirm what Angus was saying, to the limits of my ability to > measure. One of the things that I can measure is the source voltage. I have a > hacked together 12v supply. When hooked up to the 260, it initially reads just > over 9v. As it warms up, it eventually tops out just under 10v. There appears > to be roughly four different points, around 9.1v, 9.35v, 9.8v and 10v. The 260 > starts at around 9.1v, quickly moves up to 9.35v and after a while to 9.8v. It > will then sometimes move briefly up to 10v and back down to 9.8v. > > I interpret this as different heating stages - probably both ovens on, one > oven on, some sort of maintenance heating point and no heaters on. > > What I find as I adjust the pot (after letting the 260 warm up) is that > turning the pot counter clockwise the supply voltage will go up to 10v and > turning it clockwise it will drop to 9.35v or 9.1v. So, from that it would > appear that you are right in that the temperature set points are being > adjusted by the pot. Whether only one is adjusted or both are changed as Angus > says isn't clear. > > I also noticed that the 260 consistently has an adjustment range of +/-2e-7, > regardless of where the frequency is set, with 0v applied to the adjustment > pin giving a frequency 4Hz higher than when the 5.65v reference voltage is > applied to the adjustment pin. It will adjust further if the reference pin is > hooked up to the supply voltage. > > So, I decided to get as much information as I could. I turned the pot > clockwise until it "ticked" once each turn. That dropped the temperature to > the minimum. I then turned it counter clockwise 1/2 turn at a time and > recorded each temperature / frequency reading. I did this until it "ticked" > once each turn. That took nearly three days. To obtain the temperature, I > used Kapton tape to tape a temperature sensor for my multimeter to the casing > of the outer oven. This is not necessarily the hottest spot, nor does it > actually measure the temperature in either the inner or outer oven. Further, > the multimeter's precision is only around 1 degree C. The accuracy is unknown, > but it should be repeatable and roughly linear. I used my (uncalibrated) > 2465BCT to measure the frequency. This is limited to 7 digits without a > calibrated frequency standard and is probably slightly off. Still, that gave > me a good bit of data. Here is the raw data. > > 60 5.000001 > 61 5.000002 > 61 5.000003 > 62 5.000003 > 62 5.000004 > 63 5.000005 > 63 5.000006 > 64 5.000006 > 65 5.000007 > 65 5.000008 > 66 5.000008 > 66 5.000009 > 67 5.000009 > 67 5.000010 > 68 5.000010 > 69 5.000010 > 70 5.000011 > 71 5.000011 > 72 5.000012 > 73 5.000012 > 74 5.000012 > 75 5.000012 > 76 5.000012 > 76 5.000013 > 77 5.000013 > 78 5.000012 > 79 5.000012 > 80 5.000012 > 81 5.000012 > > Here is a rough graph. It shows the expected SC temperature / frequency type > of curve. However, what is interesting is the range over which adjusting the > temperature affects the frequency. This is a total of 12Hz! Also, it should be > noted that the outer case was not in place, so the outer oven is exposed to > ambient temperature. That probably limited the maximum reachable temperature. > I could noticeably change the both the temperature and frequency by simply > blowing on the 260. > > > 5.000013 * > * > 5.000012 * * * * * > * * * * > 5.000011 * * > 5.000010 * * * > 5.000009 * * > 5.000008 * * > 5.000007 * > 5.000006 * * > 5.000005 * > 5.000004 * > 5.000003 * * > 5.000002 * > 5.000001 * > > 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 > 77 78 79 80 81 > > The vendor has refunded my money for the 260 (the one that rattles), so as > soon as I get a chance I will try a new opening technique and see if it is > possible to repair it. Having learning a lot about the construction from the > first one, I think it is at least a possibility. > > I will let everyone know what happens - with pictures - once I have done that. > That may take me until next week. I am attending the Charlotte hamfest > Saturday. > > > Mike > > > > > > > > > > _______________________________________________ > 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. _______________________________________________ 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.
