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
