SX-28 infinite imedance detector mod
 

I am restoring an SX-28 that has the 6J5 Beat oscillator tube replaced
with a 6SN7GTB(Mullard!)
that is apparently working with the 6B8 2nd detector in an infinite
imedance detector arrangement. There is a switch installed next to the
tube. The radio goes silent when the switch is in one position. Do you
suppose the silent position is for operation with the original 6J5? I
don't have documentation, and tracing the modded wiring against the
original schematic is extremely difficult.
Wide bandwidth AM reception with this detector is pretty startling-
exceptional high freq response.
But poor AVC action, constant RF gain tweaking, and cranky SSB
operation appear to be the tradeoff. Does anyone have any recollection
of this mod for the SX-28? Was it documented anywhere?
Thanks!
Ben