Looking at the 1954 Modot map, I see the tower south of Hollister on Hwy 86. The symbol is an encircled brown (filled) triangle. [...]Not sure if that tower is still there or not.
I have a paper copy of the '85-'86 MoDOT map and there is still a tower in that area, but in a slightly different spot. The '54 map shows it being south of MO-86 and west of US 63, near Oasis, MO. The '85 map shows a tower on the
east side of US 63 and a little further north.
The other tower I remember was north of Rolla along US 63 somewhere. This was the last tower I went up somewhere in the 1995-2000 time frame.
There are a couple on the '85 map that might fit that description. One is on the south side of US 63, about 4 miles north of Vichy, or about 15 miles north of Rolla. The other is on the west side of US 63, about 3 miles south of Freeburg, or about 29 miles north of Rolla.
It's as if the portable radios were slow to catch up.
I have worked on a desktop early-80s synthesized Bearcat scanner, and its EEPROM required several "odd" positive and negative DC voltages to work. The scanner could run from either 120 V AC or 12 V DC, so I
think the internal power supply made about 12 V DC first, and then had another little oscillator, coil, and rectifier to make the negative voltages. It could be that the manufacturers didn't want to find room for the "extra" power-supply circuitry in a portable at that time; I'm pretty sure that as EEPROMs developed, they became able to use the same single +5 V supply as everything else, which would make them easier to integrate into a portable.