OK Barry, That is certainly the right approach to take. I thought you were already planning on what to do if the screw driver adjustment was not enough. I hope it is.
Regards, Larry On Wed, Sep 18, 2024 at 11:51 AM Barry <[email protected]> wrote: > Hi Larry, > > I'm sorry but I'm still a little confused. My intent of adjusting L701 > would be by using a screwdriver on the endpoint adjusting core. If that > doesn't give me enough range, then I presume I'd need to start modifying > the C or L values but would start with just the core adjustment. > > Thanks again, > Barry - N4BUQ > > 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
