Moon -- Some pointers to maybe help you out with the speaker terminal strip wiring:
1. R59, and R60 are both removed.
2. Capacitors C14 and C21 are re-grounded at the speaker Ground terminal so that they won't be grounded at what becomes the point where the output tube high current ground point is located. More on this later.
3. The wire from the X terminals back to V1 and V4 are removed. This leaves no leads connected to the Com or X speaker T-strip terminals in either channel.
4. All the wiring is removed from pin 3 of each output tube socket.
5. Four new leads are installed -- one from each output tube socket pin 3 up to one of the now free Com or X terminals. You want the wires from the output tubes in a given channel to go to the speaker terminal strip for that channel. As to which tube goes to which terminal within a given terminal strip is your choice. The output tubes are of stagger mounted, so in my own unit, the tubes that are staggered towards the OPT end of the chassis go to the Com terminals, since they are closest to that end of the chassis as well.
6. From each of the Com and X terminals, a precision 10Ω resistor is connected to the freed up chassis ground terminal that C14 and C21 used to be grounded to.
7. All of the wiring from the original 3 terminal test point T-Strip is then removed.
That covers the terminal output terminal strip wiring. At this point, if this is all you have done, then the amplifier will now operate as normal, but you will be able to monitor and now adjust the appropriate bias controls so that all of the output tubes each draw the same amount of current. For the stock design, this is 30 ma per tube, or .30 vdc between each Com and X terminal, and chassis ground.
Please understand that the pics from the thread on this unit were not of my own unit, but one I was temporarily sent to do just the developmental work on. Therefore, it is not my unit, nor necessarily fully restored, either. I have included pics in this post of the real unit I now own, which is a different unit from that in the pics you referenced. The modification is executed somewhat differently in my own unit, because I allowed for the addition of a choke in the B+ power supply. But for your purposes in this thread here, they are electrically basically identical. Relative to the info just given in this post, you will see that C14 and C21 remain effectively grounded at the same point that they originally were in my unit, but now done so via the ground/mount lug of a new T-strip solder-mounted onto the old chassis ground terminal. The isolated terminal on the T-strip is the new, isolated ground terminal for the four 10Ω resistors, with the ground connection for this terminal made via a lead run back to a can cap ground lug -- this eliminating any high level ground current from flowing through the chassis.
I hope none of this confuses you any further, but clarifies how the speaker terminal strips should be wired.
Dave
BELOW: Closeup of the speaker terminal strip wiring in my own SA-100.
BELOW: Closeup of the modified bias supply, and the EFB™ Screen Grid Regulator installation on and near the side wall next to the choke.
BELOW: Closeup of the complete EFB installation. Note that there's plenty of space to execute the installation without any look of clutter or being crammed in. And, without all the heat producing power resistors of the stock design, the unit runs notably cooler now, producing more power, with less distortion, and longer tube life.
BELOW: Full under-hood shot.