[R-390] R-390 VFO Question

Barry n4buq at knology.net
Wed Sep 18 10:05:21 EDT 2024 

For the R-390/URR, are they labeled as Collins or Motorola?  In other words, did Collins rebrand the Motorola PTOs or leave them branded as Motorola?  Just curious so I know who made mine.  Its label shows "Collins Radio Company".

Thanks,
Barry - N4BUQ

> On the R390/URR Collins and Motorola made PTO's.
> 
> On the R-390A/URR Collins, Progressitron, Dubrow, Motorola and Cosmos. There are
> quite a few out there with Raytheon labels, but they were rebuilt under a
> separate contract.
> 
> Les
> 
> 
> ----- Original Message -----
> From: Bob  Camp <kb8tq at n1k.org>
> To: Barry <n4buq at knology.net>
> Cc: R-390 Mailing List <r-390 at mailman.qth.net>, Larry Haney
> <larry41gm2 at gmail.com>
> Sent: 9/18/2024 7:20:55 AM
> Subject: Re: [R-390] R-390 VFO Question
> ________________________________________________________________________________
> 
>> 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
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>>>>>> 
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