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
