Fred,
Maybe I can help. My father was a field engineer for Collins Radio
from 1952 to 1955 and worked with the 18 S transmitter/receiver and 180
L antenna tuner.

I have saved things from those days for sentimental reasons. Turns out,
I have two copies of the 18S-4 instruction book. I thought it was just
an operators manual, but it's almost a half inch thick, and does have a
schematic of the set and parts list and pretty good pictures. It's a
second revision dated November 1953.

I don't need two copies, so I'll bet we can make a deal that will at
least give you some place to start without you spending your life's
savings. I'll bet Art Collins would turn over in his grave if he heard
you call his 18S-4 a "ten dollar radio".

Of interest is where did you acquire these units?

John