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

[Bob Tetrault]

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