Regulator gone bad?

Optima red top battery, (Chrome) Powermaster alternator (despite what others may say about either of these, I've had zero issues over the past few years). Use a battery tender during the winter months. When I built the car I elminated the amp guage and ran power directly from the alternator output to the starter relay lug. Have an Autometer volt gauge now.

Haven't run the car since last Spring. The day I parked it the electronic speedo stopped working and I noticed the volt gauge reading below 12 volts. Some quick checks at the time indicated normal voltage output at the alternator stud and battery. Was a hectic Summer and I finally got around to looking at it again. Battery was dead (8-9v). Because of where the car is stored right now I pulled the battery and alternator. Brought the battery back up and had the alternator bench tested. Everything looked good.

I reinstalled everything and the car starts right up but the speedo is still dead (damn). I really don't want to have to pull and send it in for repairs. A few hours later I return to do a little electrical probing. Car still starts right up but I notice the volt gauge is at 9v and will climb no higher when raising the RPMS.

I'm going to go back tomorrow and check the rest of the charging system but I'm leaning towards a bad regulator at this point. It was one of those reproduction OE units from Mancini.

Think I'm on the right track?