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 < [ mailto:[email protected] | > [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 < >> > [ mailto:[email protected] | [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 < >> >> [ mailto:[email protected] | [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 < [ mailto:[email protected] | >> >> >>> [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 < [ mailto:[email protected] | >> >> >>>>> [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 < [ mailto:[email protected] | >> >> >>>>>>> [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 < [ mailto:[email protected] >>>> >>>>>>>>> | >> >> >>>>>>>>> [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 < >> >> [ mailto:[email protected] | [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 < >> >> [ mailto:[email protected] | [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 < >> >> [ mailto:[email protected] | [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 | >> >> >>>>>>>>>>>>> http://mailman.qth.net/mailman/listinfo/r-390 ] >> >> >>>>>>>>>>>>> Help: [ http://mailman.qth.net/mmfaq.htm | >> >> >>>>>>>>>>>>> http://mailman.qth.net/mmfaq.htm ] >> >> >>>>>>>>>>>>> Post: mailto: [ mailto:[email protected] | >> >> >>>>>>>>>>>>> [email protected] ] >> >> >>>>>>>>>>>>> This list hosted by: [ http://www.qsl.net/ | >> >> >>>>>>>>>>>>> http://www.qsl.net ] >> >> >>>>>>>>>>>>> Please help support this email list: >> >> [ http://www.qsl.net/donate.html | http://www.qsl.net/donate.html ] >> >> >>>>>>>>>>> ______________________________________________________________ >> >> >>>>>>>>>>> R-390 mailing list >>>> >>>>>>>>>>> Home: [ http://mailman.qth.net/mailman/listinfo/r-390 | >> >> >>>>>>>>>>> http://mailman.qth.net/mailman/listinfo/r-390 ] >> >> >>>>>>>>>>> Help: [ http://mailman.qth.net/mmfaq.htm | >> >> >>>>>>>>>>> http://mailman.qth.net/mmfaq.htm ] >> >> >>>>>>>>>>> Post: mailto: [ mailto:[email protected] | >> >> >>>>>>>>>>> [email protected] ] >> >> >>>>>>>>>>> This list hosted by: [ http://www.qsl.net/ | >> >> >>>>>>>>>>> http://www.qsl.net ] >> >> >>>>>>>>>>> Please help support this email list: >> >> [ http://www.qsl.net/donate.html | http://www.qsl.net/donate.html ] >> >> >>>>>>>>>> ______________________________________________________________ >> >> >>>>>>>>>> R-390 mailing list >>>> >>>>>>>>>> Home: [ http://mailman.qth.net/mailman/listinfo/r-390 | >> >> >>>>>>>>>> http://mailman.qth.net/mailman/listinfo/r-390 ] >> >> >>>>>>>>>> Help: [ http://mailman.qth.net/mmfaq.htm | >> >> >>>>>>>>>> http://mailman.qth.net/mmfaq.htm ] >> >> >>>>>>>>>> Post: mailto: [ mailto:[email protected] | >> >> >>>>>>>>>> [email protected] ] >> >> >>>>>>>>>> This list hosted by: [ http://www.qsl.net/ | >> >> >>>>>>>>>> http://www.qsl.net ] >> >> >>>>>>>>>> Please help support this email list: >> >> [ http://www.qsl.net/donate.html | http://www.qsl.net/donate.html ] >> >> >>>>>>>>> ______________________________________________________________ >> >> >>>>>>>>> R-390 mailing list >>>> >>>>>>>>> Home: [ http://mailman.qth.net/mailman/listinfo/r-390 | >> >> >>>>>>>>> http://mailman.qth.net/mailman/listinfo/r-390 ] >> >> >>>>>>>>> Help: [ http://mailman.qth.net/mmfaq.htm | >> >> >>>>>>>>> http://mailman.qth.net/mmfaq.htm ] >> >> >>>>>>>>> Post: mailto: [ mailto:[email protected] | >> >> >>>>>>>>> [email protected] ] >> >> >>>>>>>>> This list hosted by: [ http://www.qsl.net/ | http://www.qsl.net >> >> >>>>>>>>> ] >> >> >> >>>>>>> Please help support this email list: >> >> [ http://www.qsl.net/donate.html | http://www.qsl.net/donate.html ] >> >> > ______________________________________________________________ >> >> > R-390 mailing list >>>> > Home: [ http://mailman.qth.net/mailman/listinfo/r-390 | >> >> > http://mailman.qth.net/mailman/listinfo/r-390 ] >> >> > Help: [ http://mailman.qth.net/mmfaq.htm | >> >> > http://mailman.qth.net/mmfaq.htm ] >> >> > Post: mailto: [ mailto:[email protected] | [email protected] ] >> >> > This list hosted by: [ http://www.qsl.net/ | http://www.qsl.net ] 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