[ARC5] BC-454-A, etc. Selectivity option found?

[D. Platt]

As fortunes would have it, I discovered a long put away McMurdo Silver  
model 805 100kHz IF amplifier, new in the box.  It purports to provide 
added selectivity to "any receiver".  It taps on to the detector plate 
and then feeds back into the audio gain pot.  I'm going to give this 
unit a try.  Has anyone here ever tried to use one of these things?  I 
don't even recall where I got it, in the first place.  I think it was in 
an estate box of stuff I once got.

Jeep - K3HVG