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
