I'm looking for information that will allow me to specifically establish date ranges for plexis and early metalface plexis by internal construction details, starting with the board types. I'm rebuilding what I now believe to be a late '68 or early '69 100 watt Plexi, and I can't be more specific than that because I never got the original back panel with serial number nor is the serial number documented anywhere. It was running when I got it, but BADLY butchered. I have a different thread regarding the restoration of this amp so I don't want to duplicate that here. But I'll be updating that thread as soon as I'm done with this post. But, look at this cleaned up chassis which shows the essential features of this specific amp in question. Small tag board near the power transformer. Main board is perforated but not in a grid pattern. Only the holes that were needed were drilled. Terminals are simple tubular terminals with lightly grooved surfaces. What year range, specifically, do these features indicate? And, the rectifier is a solid state four terminal diode bridge rectifier pack that was apparently bolted directly to the chassis originally. Here's what I started with.