Quite a long time ago Wally told me about a very simple audio derived =
AGC mod for SSB consisting of one bridge rectifier and one 10K ohm =
resistor. I tried it, didn't think it did much of anything for the =
R-390A, so I put it in a box and was going to mail it back to Wally. =
But somehow it sat for years on my kitchen counter, and never got =
mailed. Eventually I moved it to one of my parts storage closets. A =
few months ago I noticed it and decided to try it again.
The AC leads of the bridge rectifier (a 1.5 amp 50 volt Rectron RB151, =
also Radio Shack 1151) are connected to the balanced line out terminals, =
the positive lead to the ground terminal, the negative lead to a 10K ohm =
resistor lead, and the other resistor lead to the AGC jumper (either =
screw #3 or #4) on the rear panel terminal strip.
As I had done before, I turned the LINE GAIN knob to about 3. (Wally =
never told me what setting to use, and I never thought to ask.) And as =
before, I could tell that the mod was providing additional AGC voltage =
because of increased Carrier Level meter indications. And, yes, as =
before there what no noticeable improvement in the SSB quality. I still =
observed "pops" and "clicks" on some first syllables. For some reason I =
decided to increase the audio derived contribution by increasing the =
LINE GAIN setting. When I increased it to 4 and 5, SSB sounded a bit =
better. So I upped it to 6, and eventually 7. Above 7 is seems that =
the R-390A begins to be desensitized.
My opinion now of the K5OP audio derived mod is completely reversed. It =
is a great SSB mod when used in conjunction with my well-known AGC mod. =
It is also simple to do. I soldered terminal lugs (available from Radio =
Shack) to the AC and + leads of the bridge rectifier, and a short =
insulated wire from the "other 10K resistor lead to a terminal lug so =
that the mod can be implemented merely by unscrewing 4 screws on the =
terminal strips, sliding the lugs onto the screws, and tightening the =
screws. No soldering to the R-390A is necessary. Try it. You'll like =
it. It, together with my BFO vernier fine tuning mod, makes the R-390A =
a truly world class SSB receiver.
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