[R-390] Solid State R-390, Why Not?

[Bob Camp]

Hi,

Not saying you are wrong, but those numbers are about 40 db better than
what's been published elsewhere on the R-390A.

    Bob

----- Original Message -----
From: "Bob Tetrault" <r.tetrault@attbi.com>
Cc: <r-390@mailman.qth.net>
Sent: Sunday, August 11, 2002 8:21 PM
Subject: RE: [R-390] Solid State R-390, Why Not?


> Dynamic range is pretty hard to beat:
> IP3=+10dBm at 10kHz separation
> IP3=+20dBm at 100kHz separation (the difference is in the tunable front
end)
> 4dB noise figure on all bands.
>
> One can buy receivers with better IP3 numbers, but they don't have a 4dB
> noise figure. It's debatable whether or not anyone can use 4dB, since it's
> commonly thought that the HF noise level is 10+dB, but that isn't always
the
> case...and we watch and wait for those openings...
>
> One could experiment with pushing the distortion levels even further down,
> but it requires pushing the tubes harder since the standing current
> determines their threshold of distortion. Turning up the juice means
they'll
> exhaust the cathode emission sooner.
>
> Having extra modules does give anyone the option to play all they want.
I've
> heard that ome people have replaced the first two mixers with 7360
designs;
> this is a double balanced tube mixer designed for SSB detection and
> generation. Rumor has it that they are noisier than the 6C4W, but I've
never
> seent the numbers or methodology. How much it improves the front end is
also
> anecdotal. There was a considerable body of literature about similar mods
to
> the 75A4, since that receiver was/is(to some, even now) considered one of
> the best DX'ing receivers around. Again, my exposure never got beyond the
> anecdotal level, though I'd relish a review of all that was published on
> that topic. If memory serves, there was quite a lot in QST and CQ back in
> the 60's and early 70's. Anyone got any numbers on this mod?
>
> The drawback to modifying an RF deck is the RF deck, as anyone who has
ever
> taken one out will attest.
>
> But let's remember that there were 50K of these made, and while there are
an
> uncounted number of them that were lost, stolen, spindled, stapled and
> mutilated, modifying one is a drop in the bucket.
>
> Imagine what a great exciter a 390 would make! Imagine a pushbutton where
> the diode load is so that you could zero-beat a carrier.
>
> pot-stirring in Portland,
>
> Bob
>
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