Just in case anyone is interested:

I got tired of looking / waiting for the "real" SSB adapter for the
R-390A ( or a usable substitute ) and didn't want to put any mods into
my radio. Here is my fast and semi-dirty solution. It provides an
external adapter that works from the 455KC 50 ohm IF output on the
rear of the R-390A.

I bought a bad Yaesu FRG-7700 general coverage receiver off of ebay.
It had a destroyed display section, but was otherwise ok.

I disconnected the cable from the antenna connector and ran a wire
from the connector and through a shiny new bright orange .047 uF cap
to the collector of Q-23 (which is actually on the secondary center
tap of T-09). Then I just ran a cable from the IF out of the
R-390A to the antenna input connector on your new adapter. End of mod.

You now have selectable USB/LSB/AM(with 3 bandwidths), 3 more IF amps,
usable AGC (kinda), S-meter, and Audio amp with speaker, phone jack,
recorder output and tone control. It works great.

If you are using a working FRG-7700, you could leave the radio intact
and add a bnc connector to run the IF input. I decided to gut the
rest of the Yaesu out and have a stand alone, no extra knobs, adapter.
I removed the entire PLL / logic board (??? whatever they call the
bottom board ) and everything that wasn't related to audio, IF, and
the product detector. This left the top board , power supply and
audio stuff.

My scientific approach to eliminating unneeded circuitry was listening
to the R-390A through the adapter and one at a time unplugging
internal connectors in the 7700. If nothing stopped working I left it
unplugged and went on to the next connector. After doing that I
removed all disconnected cables and any boards that no longer had
anything hooked to them. These boards were then sold on Ebay (boards,
VFO, memory board etc)

If anyone else has already done this, I'm sorry I claimed credit for
the idea.... havn't heard of it anywhere before. The same idea could
probably be done using any old receiver with a 455 IF and product
detection at that frequency.

E-mail any questions or comments to:

73
Bob WB8CAC
http://www.qsl.net/wb8cac