I know for existence of this product, nice piece of electronics but unfortunately this is not what I am looking for. I want to built detector by myself, using my knowledge and patience for homebrew electronics...Beside of this detector, and one from Surrey will be possible to find some other somewhere on the net or in drawer?
Pozar, Bob from Treetop Circuits wanted me to advise you of the following, maybe this could still help you with your request.
The circuits used in our products are (as you know) fully described in our instruction books, which can be downloaded from our website. We have no objection to folks copying them for their own use. If he replicates some or all of the SB-390 circuitry, and adds a BFO and a 24-volt AC supply, he'll have a good "outboard" adapter that will perform as well as the SB-390. I'd recommend a BFO with some range of adjustment, because the best results are obtained when it's adjusted to the right frequency relative to the mechanical filter.
I really like the 4-diode detector because it has a soft clipping action when overloaded. You can get quite good results even with no AGC. You have to "ride" the RF gain, but it's much more forgiving than the detector in the R-390.