I experienced the AC30X a couple of times in my early career, firstly our bass player had one when I worked beiefly in an outfit called The Four Blades in Sheffield just before I turned pro with Frankenstein & The Monsters (what a load of crap that was) anyway back to the amp. It was used with an Epiphone Rivoli bass and sounded bloody good with it's fifteen inch speakers compared to what we had heard before. I'm sure it had a Top Boost circuit as well.
The second time I came across one of these beasts was when I saw The Cresters from Leeds during 1964, with the amazing Richard Harding on lead guitar. He used a Grestch White falcon through a Green Binson Echo unit and sounded more like Chet Atkins than Chet himself - absolutely red hot ! Richard sold the White Falcon and used a Country Gent for a long time and if anyone fancies seeking him out, I understand he is still playing in a band called 'Derringer' now using a Telecaster with a Fender Twin if I remember correctly.
There was a Vox AC30X for sale at Shadowmania around 2005-ish, I remember seeing it opposite the Burns stand and those memories came flooding back, I often wonder who bought it?