Close to the 1965 version but equipped 2x12, with the original manufacturer of 2xG12T75 16ohms in parallel. Compared to the 1965 which is 4xG10L35, it gives less possibility of evolution, such association with 2xG10L35 2xG12 choice.
The 1966 is roughly equivalent to 1922, but application documents for Mosfet or Valvestate head, ie a width of 60cm.
Among my various versions of 1965, I bought a 1966a. I changed it to cut two slots Popuri accommodate two 10-inch G12 plus.
So if I had the choice again, I would rather a 1965, rather than having to fiddle around then, so I do not put that 8 / 10 when I put 9 / 10 for 1965 ...