[R-390] R-390 VFO Question

Barry n4buq at knology.net
Wed Sep 18 07:58:46 EDT 2024


That first line should have been:

Regarding the tutorials, I'm wondering which, if any, might apply to the PTO in the R-390/URR.

Thanks,
Barry - N4BUQ

> 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