[R-390] R-390 VFO Question
Barry
n4buq at knology.net
Wed Sep 18 09:54:14 EDT 2024
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 <n4buq at knology.net> 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 <n4buq at knology.net> 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 <n4buq at knology.net> 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 <72volkswagon at gmail.com> 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 <larry41gm2 at gmail.com> 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 <72volkswagon at gmail.com>
>>>>>>>>> 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:R-390 at mailman.qth.net
>>>>>>>>>>
>>>>>>>>>> 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:R-390 at mailman.qth.net
>>>>>>>>
>>>>>>>> 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:R-390 at mailman.qth.net
>>>>>>>
>>>>>>> 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:R-390 at mailman.qth.net
>>>>>>
>>>>>> This list hosted by: http://www.qsl.net
> >>>>> Please help support this email list: http://www.qsl.net/donate.html
More information about the R-390
mailing list