I took the PTO out and rigged a setup where I can rotate the shaft exactly ten turns while monitoring the output frequency.
Thinking I needed less L, I tried rotating the endpoint adjustment 1/4 turn CCW. That decreased the overall frequency change by a small amount which was the wrong direction I needed. I then rotated it 1/2 turn CW (effectively 1/4 turn CW from the starting point) and that got me to about 998 kc on ten turns. Another 1/4 turn CW and I got exactly 1000 kc on ten turns. I don't know what the linearity is yet but I can check that at 50 kc and 100 kc intervals while I still have it out. Thankfully, it was quite easy to do this. Thanks to all who replied. Barry - N4BUQ > 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
