Circuit Board Variations
I'll leave you to check out the differences in the four photos below. After all, you've got to be a chronic if you are interested in spending that long viewing this page anyway.
Here's the Revision "D" circuit board from my dark green TR-6. The relatively straight and simple print pattern used certainly suggests it is an early design. We also see loads of hand-soldering used to finish the circuit board. The partially obscured uppercase letters, (initials?), that read "TN" in the upper right corner are also something found on other early Totsuko circuit boards, such as the TR-5. However, the unit this board came from has a serial number later than the two on this site with Rev. G boards in them. Probably just an example of an early board finding its way into production later because parts are tight so it was needed, or it was recycled, built for somebody sepcial, etc.
While working with the earliest of the "G" revision circuit boards, Totsuko is obviously still developing the whole process of using printed circuit boards. And, while doing loads of soldering on the board, they are still exploring to find where to improve (or fix) the design of the board for the TR-6. Yep, all that solder is original, including that running down the length of the vertical print trace just to the left of the center of the board. They were also compelled to cut away the printed trace in one location and add a "bridge". (It's on the right where the two resistors have been added).
While the design is roughly the same as with the "G" revision, the "I~1" revision shows how much progress Totsuko had made with printed circuit board production by the end of 1956.
The electrical design of the later R-6D2-A revision circuit board marks a complete digression from the original TR-6. In fact, while it is found in the last TR-6 units produced, it is the circuit board more commonly found in and related to the TR-66. Without getting into details, the printed side shows at a glance how greatly the print traces have been simplified and rationalized.