Hi Barry, I believe that the total range of adjustment of L701 is about 7.5 kc (5 turns of wire). If you needed to only adjust it 1-2.5 kc to get it back into range, I'd probably go the route of removing 1-2 turns, but at about 1.5 kc per turn, you'd need to remove 3 turns and that makes the adjusting range quite small after that. It's doable, but a little restrictive.
Regards, Larry On Wed, Sep 18, 2024 at 10:52 AM Barry <[email protected]> wrote: > 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
