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
