Bob, Per Figure 8 of the SX-28A manual (and I'm sure it will be the same for the non-A SX-28), the 6SA7 Mixer, V3, is the third tube from the back of the chassis in the line of tubes between the two tuning capacitors. And yes, pin 8 or terminal 8 on the socket would be the right place to inject a signal for alignment. Jim Hanlon, W8KGI