[R-390] Re:R390(A) - S.S.B.

[Kenneth G. Gordon]

Years ago, for a special project at the University of Idaho where I 
work, I added a fairly easily removed mod to an R-390 wherein I 
used 1/2 of the 12AX7 (IIRC) which fed the IF out to the jack on the 
back, as a triode product detector. The detector circuit I used, the 
same circuit used in Heathkit's SB/HW transceivers, actually looks 
more like an "infinite impedance detector" than a true product 
detector as such, since it seemed to work equally well for AM as for 
SSB. In any case, it was much quieter than the diode detector and 
was pretty effective. The mod took very few parts, worked quite 
well, and was easily removed if you wanted to.

I didn't bother with changing the AGC time constant. I just kept the 
RF gain down a bit, and ran the audio gain up.

I had used the same circuit back in the 1960s in another R-390 we 
were using as the receiver for 'phone patching for the troops in 
Vietnam and Thailand when I was in AFMARS, and in a BC-779 
which I used for RTTY.

I've never liked the 6BE6 for anything since it is so noisy. The only 
mixer tube I know of which was noisier was the 6K8/12K8, but I 
think there are noisier tubes than those.

Rambling.....

Ken Gordon W7EKB