I looked for common tubes and circuits between the NC-300 and the later receiver the NC-303.
Figured the NC-303 was an upgraded and redesigned NC-300 and that improvements to the common stages like the IF and the RF stages would be useful.
Mostly seems that the cathode resistors were lowered in resistance to provide more gain?
Net result is that this NC-300 acts now more like the NC-303 which I had fixed and sold.
Mods:
1) added .1uf capacitor to ground on T6 pin "A". Per NC-303 schematic.
2) V4 Pin #7 330 ohm to 1200 ohm resistor
3) V9 pin #3 to ground
4) V9 pin #8 1.3K resistor to 820 ohm resistor
5) V2 pin #3 resistor 470 ohms to 180 ohms
6) C130 add 1uf capacitor to mode switch for SSB LUG (lug empty on NC-300) NOT IMPLEMENTED as too hard to access mode switch.