[Collins] R-388/51J mods - BCB included

[Bill Cotter]

That's a good point about the value chosen, Jerry.

I think a much lower value would be a better choice for matching 
and keeping the mixer happy. The value 0.0iuF was likely a 
'brute-force' option. This mod was conceived a long time ago, and I 
cannot remember the source (CQ or QST, I believe). Howard Mills, 
W3HM, brought it to my attention when I was working out the kinks 
of this receiver.

73 Bill



>There might be a compromise value that gets some increased gain 
>without
>driving the mixer so hard and compromising the intermod range with
>strong signals. I suspect the small coupling capacitor was chosen to
>limit the effects of strong signals characteristic of domestic 
>locations
>on the broadcast band while giving sensitivity some better than the 5
>tube AC/DC kitchen radio. I'm thinking 30 to 100 pf might give 
>adequate
>gain without hurting the strong signal handling too much.
> >
> > Another useful mod for the BCB listener is to increase band-1
> > sensitivity by increasing RF/1st mixer coupling. Parallel a .01uF
> > across C117 (3pf).