Sorry. The first line of that last paragraph had kc where it should have been MC (or Mc or MHz or...):
I don't how the counter now shows 499.7 for the VFO set at 2.9550 MC and, conversely, the VFO frequency at 500.0 is now at 2.9548 MC. Thanks, Barry - N4BUQ > Previously, I mentioned I have the endpoint data. > > VR Counter VFO Frequency (in MC) > ---------- --------------------- > +001.4 2.4550 > 499.7 2.9550 > -997.4 3.4550 > > That makes the counter span for 1000 kc of the VFO to be 1000 + 1.4 + 2.6 = > 1004 > kc. > > Switching to zeroing the VR counter at both ends: > > VR Counter VFO Frequency (in MC) > ---------- --------------------- > +000.0 2.4566 > 500.0 2.9548 > 000.0 3.4524 > > That makes the VFO span for 1000 kc on the counter to be 3452.4 kc - 2456.6 > kc = > 995.8 kc so 4.2 kc short. Hopefully the endpoint adjustment still has that > much left in it and I won't need to open the can and perform any surgery. > > I don't how the counter now shows 499.7 for the VFO set at 2.9550 and, > conversely, the VFO frequency at 500.0 is now at 2.9548 kc. Something must've > moved just a tiny bit since I set it. > > Thanks, > Barry - N4BUQ > >> 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 ______________________________________________________________ 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
