[R-390] R-390a SS Conversion

[Alan Victor]

Thanks all for the replies. This topic... conversion of some of the top of
the line BA's to solid state would make a great special interest users
group! Taking on a unit like the R390 or the A certainly makes sense in
that the mechanical and the tunable selectivity is so brilliant, it's hard
to duplicate today. However, of course today we skin the cat in a different
manner. Try to emulate as much of that capability with sophisticated
devices and I suppose today it is done quite well. I have designed and
built from the ground up several receivers and they all play quite well.
But, I keep dabbling cause they are NOT anywhere perfect! That said, I
consider what Mack and Charles and whomever takes on this task, a tip of
the hat. Consider your starting off with a pretty extraordinary radio, you
could wind up with the best of the best!

GL, Alan W4AMV

On Sat, Oct 30, 2021 at 7:32 PM Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> The risk in doing this is that (even with a JFET cascode) the output
> impedance of
> the solid state stage is much lower than tube it replaces. At the same
> time the Gm
> of the JFET stage is (potentially) much higher than the Gm of the tube.
>
> You can get the gain worked out and have the Q of the input or output
> tanks very
> different than in the original design.
>
> Does any of that apply to this attempt? No idea ….
>
> Back in the day, one could get HF compatible small signal MOSFET’s. Not so
> much
> these days. The JFET cascode is how it’s done ….
>
> Bob
>
> > On Oct 30, 2021, at 6:41 PM, Mack McCormick <w4ax.mack at gmail.com> wrote:
> >
> > Alan,
> >
> > I did not map out the impedance levels, perhaps Charles did. All stages
> are
> > solid state. MPF102 JFETs. The original power supply is removed and the
> > radio electronics are run on 24VDC. I did take several gain measurements.
> > There was a real problem with getting the gain of the 1st IF correct.
> > Coupling between stages is pretty critical.
> >
> > Mack
> > W4AX
> >
> > On Sat, Oct 30, 2021 at 12:31 Alan Victor <amvictor at ncsu.edu> wrote:
> >
> >> Hello Mack.
> >>
> >> Curious if you and Charles mapped out the various impedance levels and
> >> required gain from stage to stage? Did you convert every stage to SS or
> >> targeted specific ones?
> >>
> >> Apologize if this question is answered in one of your posts.
> >>
> >> Thanks for the info!
> >>
> >> Best73' Alan W4AMV
> >>
> >> On Sat, Oct 30, 2021 at 6:55 AM Mack McCormick <w4ax.mack at gmail.com>
> >> wrote:
> >>
> >>> Perry,
> >>>
> >>> Charles provides an excellent template to SS your R-390a. He is a
> >>> wonderful gentleman and we collaborated often. I am the only other
> known
> >>> person to complete the project. Charles and I went through four design
> >>> changes as I SS's a R-390a. It is a rock solid design now.
> >>>
> >>> Without knowing your technical/construction skills let me caution this
> is
> >>> not a trivial project and requires at least intermediate level skills.
> >>>
> >>> I posted about my SS conversion on this list within the past three
> months.
> >>> You can search for the thread if interested.
> >>>
> >>> Here are pictures of some of my work. Please note: The PC boards I made
> >>> for
> >>> the SS tube replacements are no longer the current design. I will
> provide
> >>> you with the version 1 files but you will need to update them to the
> >>> latest
> >>> design using KiCad (free on DigiKey).
> >>>
> >>> Good luck and I'll be interested in your results if you undertake this
> >>> project.
> >>>
> >>> https://photos.app.goo.gl/11AjyNCi2zV3T8LaA
> >>>
> >>> 73,
> >>>
> >>> Mack
> >>> W4AX
> >>> https://www.qrz.com/db/W4AX
> >>> ______________________________________________________________
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> >>>
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> >>>
> >> --
> >
> > 73,
> >
> > Mack
> > W4AX
> > https://www.qrz.com/db/W4AX
> > ______________________________________________________________
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>