[R-390] SP-600 Product Detector

[N4BE_Jim via R-390]

I used to have a SP-600 JX-something in 1970 or there abouts.  Got it from MARS.  Wish I still had it, but I gave it away.  Anyway, 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.   I also had an audio-derived fast attack slow decay AGC, which I think used an extra triode in the 12AU7 product detector tubes.  Worked pretty good.

Jim N4BE