[R-390] R-390 VFO Question

Wed Sep 18 11:30:39 EDT 2024

Hi Larry,

Thank you so much for pointing to that document.  I now see the endpoint
coil, the corrector stack, etc., in very clear photos.  Hopefully just a
simple endpoint adjustment will get me close enough but won't know until I
get that adjusted.

Thanks again,
Barry - N4BUQ

On Wed, Sep 18, 2024 at 9:14 AM Larry Haney <larry41gm2 at gmail.com> wrote:

> Hi  Barry,  Since the 390 PTO is mechanically the same as the 390A PTO made
> by Collins (has the corrector stack on the inside), the document I wrote on
> the Collins 390A PTO should be applicable to the 390 PTO.  Here's a link to
> it in the tutorials section: R390A My Collins PTO Observations
> <https://www.r-390a.net/R390A_My_Collins_PTO_Observations.pdf>.  I think
> Collins was the only manufacturer of the 390 PTO.  FYI - removing a turn
> off of the EP adjustment coil, L701 reduces the EP adjustment range.  This
> can be a problem in the future when readjustment is necessary.
>
> Changing the ratio of L to C can put a linearity bubble in the middle of
> the range.  Small changes should not be an issue.  Also, removing the
> covers off of the PTO changes the operating frequency quite a bit, but is
> restored when replaced.  And, adjusting  the 'stack' is quite challenging.
> Unless something specific has happened to it, its current state should be
> OK.
>
> Working on the internals of these can be frustrating and time consuming -
> be prepared.
>
> Regards, Larry
>
> On Wed, Sep 18, 2024 at 4:58 AM Barry <n4buq at knology.net> wrote:
>
> > 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
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