I think I remember the number from the dlate 1960s but can't recall what
their main use was, refreesher?

Hank-

The RCA 40673 Dual Gate MOSFET was used as a low noise VHF RF Preamp in the
early 1970s. There were at least two preamp kits popular at the time, such as
the one from Topeka FM & Engineering. I used such a preamp on my Regency
HR-2A, supposedly improving the sensitivity from 0.35 uV to 0.2 uV. Of course
there was an increase in intermodulation interference that came with it!

While there are many such pieces of equipment still in use, there are newer
devices that can be used as a replacement for the 40673. An example (only
slightly newer) is the 3N201.

Today's FM rigs typically have better sensitivity even without an additional
preamplifier.

73, Fred, K4DII