These read something like T020366 or F034267 where the "66" and "67" denote the year and the "03" and "42" denote week of the year.Of course, the most foolproof way is to pull the chassis and look at the layout.
Rabe was known for his engineering work at Acoustic Control Corporation.
In 1986, SWR released the Goliath, a 4 x 10" full-range speaker cabinet with a built-in horn tweeter, a first for bass cabinets.
Part of the confusion stems from the lack of any AB568 or AC568 tube charts.
Fender never printed any since there were plenty of leftover AB763 tube charts available and these were used well into 1969.
The cosmetics of the silverface amps during the transition between circuits was also in transition making it difficult to determine circuit type on cosmetics alone.