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
