Hi Larry, I'm curious why changing out a cap would be the first line of effort. Is that because there may not be enough change available from L701 to correct for 4 kc?
Thanks, Barry - N4BUQ > Hi Jim, Yes, I've done that and it works quite well. > > Barry, Since the EP is about 4kc off, I'd suggest using the capacitor > adjustment method because removing 1 turn off of the L701 is not going to > be enough. Removing 2 turns really limits its adjustment range. Be very > careful with those 10 pf caps inside the pto, they are very fragile. You > should be able to calculate fairly close as to the value to put in series > with a 10 pf, and give it a little wiggle room for adjustment. > > Regards, Larry > > On Wed, Sep 18, 2024 at 9:07 AM Jim Whartenby via R-390 < > [email protected]> wrote: > >> Since the trend is a reduced frequency range, something has obviously >> increased in value internal to the PTO. There are two inductors and three >> capacitors in the circuit. The inductors have two ferrite cores so there >> are seven components in total that determine frequency. I have the feeling >> that the ferrite permeability has increased over time perhaps due to >> shrinkage. I don't see how either coil can have increased in inductance >> without causing binding with their respective ferrite cores. Of course it >> is still possible that any or all of of the tank capacitors could have >> increased in value. >> >> I assume that the two 10 pF capacitors have either a positive or negative >> temperature coefficient of different slopes to compensate for the operating >> temperature of the PTO. Lifting one of the two 10pF caps and placing, for >> example, a 100 pF NPO in series with it will subtract 1 pF from the total >> tank capacitance and raise the operating frequency without significantly >> changing the temco. This should preserve the end point coil inductance >> range. Has anyone tried this instead of removing a turn on the endpoint >> coil? >> >> Jim >> >> Logic: Method used to arrive at the wrong conclusion, with confidence. >> Murphy >> >> On Wednesday, September 18, 2024 at 10:04:39 AM CDT, Barry < >> [email protected]> wrote: >> >> 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 >> ______________________________________________________________ >> 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
