I'll answer one question.
You can't turn off the preamp. There's a patent that was granted for this design. It puts the four 6BQ5 tubes in line with the antenna and the receiver.
A four-tube preamp. No joke. A really noisy preamp, to boot.
Two drawbacks to this.
First, you can't leave it in line and use the radio unless the LR is turned on and running. There is no standby.
Second, the preamp will cause receive problems.
Leads me to wonder how they sold more than a dozen of them in the first place.
I'll have to look up the patent number. Closest you'll get to a schematic, most likely.
73