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
