Hi Using a impossible extreme case to keep the math easy:
If your PTO covers (say) 900KHz rather than 1000 KHz, there will be a 100KHz “gap” that you can not tune to. Any significantly “too small” range would have the same impact. (Yes, there is a bit of extra travel at the ends of the range so this does not get totally insane ….). Bob > On Sep 18, 2024, at 9:54 AM, Barry <[email protected]> wrote: > > Would a significant difference in span between bands be due to the first > crystal oscillator? Otherwise, I'm not sure how that would occur. > > Thanks, > Barry - N4BUQ > >> Hi >> >> As long as the end points still line up so you have a 1000 KHz span with one >> being at 2955, the radio should be in reasonable shape. Having a “gap” >> between >> bands ( = a < 1000 KHz span) would be a PIA …. Fortunately that rarely is the >> case. >> >> There are still piles of R-390A’s sitting here or there …. >> >> Bob >> >>> On Sep 18, 2024, at 9:39 AM, Barry <[email protected]> wrote: >>> >>> I set the PTO's frequency per the manual (i.e. set the VR counter to any >>> 500.0 >>> reading and adjust the PTO to 2955 kc. The endpoint on the low side is >>> different from the endpoint on the high side so I'm presuming I have just a >>> bit >>> of non-linearity; however, I think if I get the endpoints set to an even >>> 1000 >>> kc, then any non-linearity will hopefully be minimal. I'm not all that >>> concerned if the minor divisions aren't exact and will live with it as long >>> it's not too much. The trouble to tweak that may be much more effort than >>> it's >>> worth to me. >>> >>> I wish I could've seen some of those "mountains"! I've seen pictures of the >>> stacks of blue-striper R-390A/URRs that sat out in the rain. Sad. >>> >>> Thanks, >>> Barry >>> >>>> Hi >>>> >>>> The gotcah is that the internal adjust coil may not have enough range to >>>> get the >>>> PTO back to where it needs to be. You may need to get a bit creative. >>>> Better to >>>> do this *before* any of the other work. >>>> >>>> This is not a new issue. Back in the day, the military spent a lot of time >>>> and >>>> money swapping out PTO’s. It was cheaper / easier to do that than doing a >>>> full >>>> rebuild. There are stories of “small mountains” of PTO’s building up behind >>>> repair depots as a result. Like any story, the size of those mountains >>>> likely >>>> got bigger and bigger with each telling of the story :) :) :). >>>> >>>> Bob >>>> >>>>> On Sep 18, 2024, at 8:28 AM, Barry <[email protected]> wrote: >>>>> >>>>> Hi Bob, >>>>> >>>>> I see where the PTOs for the R-390/URR and R-390A/URR both have end point >>>>> adjustments. L701 performs that in both. The schematic I see for the >>>>> R-390A/URR conveniently labels that as such on the schematic. RM >>>>> 11-5820-357-35 calls it out on page 12, Paragraph 12-b defines the >>>>> function of >>>>> that coil. I just wasn't seeing that last night. I sure wish I had a >>>>> searchable PDF for the R-390/URR's service manual. >>>>> >>>>> Thanks, >>>>> Barry - N4BUQ >>>>> >>>>>> Hi >>>>>> >>>>>> Motorola most certainly made their own PTO’s for the radios they >>>>>> supplied. Long >>>>>> ago I talked to the folks who did the linearity adjustments on them. >>>>>> They still >>>>>> had (not so) fond memories of doing those adjustments. >>>>>> >>>>>> Bob >>>>>> >>>>>>> On Sep 17, 2024, at 11:29 PM, Barry <[email protected]> wrote: >>>>>>> >>>>>>> Hi Larry, >>>>>>> >>>>>>> Regarding the tutorials, I'm wondering which might apply to the PTO in >>>>>>> the >>>>>>> R-390A/URR. I see most(all?) of them are regarding the COSMOS units >>>>>>> but am >>>>>>> wondering which PTO is in the R-390/URR and whether any of the >>>>>>> rebuild/linearity documents apply to that one. Were all the R-390/URR >>>>>>> PTOs >>>>>>> made by Collins and no COSMOS in that version? >>>>>>> >>>>>>> Mine is running just a bit fat - maybe 1.5 kc end-to-end. I have the >>>>>>> actual >>>>>>> numbers written down and can post that when I get back to the >>>>>>> workbench. From >>>>>>> what I remember, removing a turn shortens the end-to-end but perhaps >>>>>>> additional >>>>>>> C would work as well. I don't know what effect that might have on >>>>>>> linearity >>>>>>> but I don't think it should. >>>>>>> >>>>>>> The R-390A/URR PTO has an endpoint adjustment. Does this exist for the >>>>>>> PTO in >>>>>>> an R-390/URR? >>>>>>> >>>>>>> Thanks, >>>>>>> Barry - N4BUQ >>>>>>> >>>>>>>> Hi Barry, I thought what you wrote makes sense and is correct. It's >>>>>>>> good >>>>>>>> that you are understanding how it all works. It makes diagnosys so >>>>>>>> much >>>>>>>> easier. Good going. >>>>>>>> >>>>>>>> If you're interested in more reading on the 390A PTO's, there are 3 >>>>>>>> docs on >>>>>>>> our website in the repair tutorials section by Tom Marcotte, Jim >>>>>>>> Miller and >>>>>>>> myself. >>>>>>>> >>>>>>>> Regards, Larry >>>>>>>> >>>>>>>> On Mon, Sep 16, 2024 at 5:51 AM Barry Scott <[email protected]> >>>>>>>> wrote: >>>>>>>> >>>>>>>>> Okay, Larry. Thanks for the reply. >>>>>>>>> >>>>>>>>> On further reading, the VFO is a Hartley design and, given that the >>>>>>>>> frequency formula for a Hartley is an inverse function of the LC >>>>>>>>> values, >>>>>>>>> presuming that at xx 000, the iron core is "out" of the coil and a >>>>>>>>> clockwise turn of the KC knob causes the core to be pushed further >>>>>>>>> inside >>>>>>>>> the coil increasing the L, then the frequency would indeed drop with >>>>>>>>> CW >>>>>>>>> motion of the knob. Sorry for the awkward way of stating that but I >>>>>>>>> think >>>>>>>>> it makes sense to me. >>>>>>>>> >>>>>>>>> Thanks again, >>>>>>>>> Barry - N4BUQ >>>>>>>>> Thanks, >>>>>>>>> Barry - N4BUQ >>>>>>>>> >>>>>>>>> >>>>>>>>> On Sun, Sep 15, 2024 at 11:10 PM Larry Haney <[email protected]> >>>>>>>>> wrote: >>>>>>>>> >>>>>>>>>> Hi Barry, You are absolutely correct in your deductions. When the >>>>>>>>>> KC is >>>>>>>>>> at its lowest of 000, the vfo is at its highest (3.455 mh). >>>>>>>>>> >>>>>>>>>> Regards, Larry >>>>>>>>>> >>>>>>>>>> On Sun, Sep 15, 2024 at 7:23 PM Barry Scott <[email protected]> >>>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>>> Looking at the simplified schematic for the 3rd mixer (V205), the >>>>>>>>>>> output >>>>>>>>>>> from the 2nd mixer (V204) tunes from 3 to 2 MC and the VFO tunes >>>>>>>>>>> from >>>>>>>>>>> 3.455 >>>>>>>>>>> MC to 2.455 MC yielding a constant 455 kc mixer product. Is it >>>>>>>>>>> correct >>>>>>>>> to >>>>>>>>>>> interpret those numbers to mean that if the counter starts at XX >>>>>>>>>>> 000 >>>>>>>>> and >>>>>>>>>>> the KC control is rotated CW to XX +000 the VFO's output frequency >>>>>>>>> starts >>>>>>>>>>> at 3.455kc and falls 1000 kc for 10 turns CW on the KC knob? >>>>>>>>>>> >>>>>>>>>>> I'm asking because I want to know what the frequency of the VFO is >>>>>>>>>>> supposed >>>>>>>>>>> to be when the dial is at XX 000 and I presume it's 3.455 kc but >>>>>>>>> wanting >>>>>>>>>>> to make sure. >>>>>>>>>>> >>>>>>>>>>> Thanks, >>>>>>>>>>> Barry - N4BUQ >>>>>>>>>>> ______________________________________________________________ >>>>>>>>>>> R-390 mailing list >>>>>>>>>>> Home: http://mailman.qth.net/mailman/listinfo/r-390 >>>>>>>>>>> Help: http://mailman.qth.net/mmfaq.htm >>>>>>>>>>> Post: mailto:[email protected] >>>>>>>>>>> >>>>>>>>>>> This list hosted by: http://www.qsl.net >>>>>>>>>>> Please help support this email list: http://www.qsl.net/donate.html >>>>>>>>>>> >>>>>>>>>> >>>>>>>>> ______________________________________________________________ >>>>>>>>> R-390 mailing list >>>>>>>>> Home: http://mailman.qth.net/mailman/listinfo/r-390 >>>>>>>>> Help: http://mailman.qth.net/mmfaq.htm >>>>>>>>> Post: mailto:[email protected] >>>>>>>>> >>>>>>>>> This list hosted by: http://www.qsl.net >>>>>>>>> Please help support this email list: http://www.qsl.net/donate.html >>>>>>>> ______________________________________________________________ >>>>>>>> R-390 mailing list >>>>>>>> Home: http://mailman.qth.net/mailman/listinfo/r-390 >>>>>>>> Help: http://mailman.qth.net/mmfaq.htm >>>>>>>> Post: mailto:[email protected] >>>>>>>> >>>>>>>> This list hosted by: http://www.qsl.net >>>>>>>> Please help support this email list: http://www.qsl.net/donate.html >>>>>>> ______________________________________________________________ >>>>>>> R-390 mailing list >>>>>>> Home: http://mailman.qth.net/mailman/listinfo/r-390 >>>>>>> Help: http://mailman.qth.net/mmfaq.htm >>>>>>> Post: mailto:[email protected] >>>>>>> >>>>>>> This list hosted by: http://www.qsl.net >>>>>>> Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ R-390 mailing list Home: http://mailman.qth.net/mailman/listinfo/r-390 Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
