[R-390] SP-600 Product Detector

[Charles Steinmetz]

Jim wrote:

>I added a tube based product detector using a schematic from an ARRL 
>handbook of that era.  You might look there if you want vintage.

Good search skills should turn up at least four SP-600-specific tube 
product detector mods circulating on the internet.  One (from QST 
many years ago) uses a 6J4 with grid and cathode injection, one uses 
a cathode-coupled 12AU7 (essentially a Pullen mixer) with the 
existing BFO, one uses a similar cathode-coupled 12AU7 with a new 
12AT7 crystal-controlled BFO, and one uses a 6BY6 pentagrid converter.

I have not built or even carefully reviewed any of these designs and 
cannot comment on how well they may or may not work.

Best regards,

Charles