The Vox Recording Studios - 15456 Cabrito Road
Late summer 1968 to summer 1969.
It is interesting to find that in the documentary on "Sound City" Studios (on Amazon Prime) and on this website, the Studios' building is said to have been the place where Vox instruments - i.e. those made by "Thomas Organ" - were assembled. In actual fact, 15456 Cabrito Road had been the Thomas Organ "Soundlab" - the "Vox Recording Studios". "Sound City" therefore took over an existing studio complex rather than a Thomas assembly line.
"Sound City Studios" in the 2000s.
The main Thomas complex was at Hayvenhurst Avenue on the other side of Van Nuys airport - see this page.
The creation of the "Soundlab" corresponds pretty well with the shake-up of the "Vox Division" in the summer of 1968. See the foot of this page.
Below, the Thomas promotional brochure, presumably issued at some point close to August '68. Thanks to Glen Beauchamp for the pictures.
By late 1968, the "Soundlab" had become the "Vox Recording Studios". Whether someone had to change the name at the studio entrance is not known.
"Billboard" magazine, 31st December, 1968. "All you have to bring is your talent" - a great line.
At present, the latest mention of Thomas in connection with the premises seems to be from August 1969 ("Billboard" magazine, 30th August, 1969), but as that is just a list/directory of studios, the reference to Thomas's being there could well be out of date.
For the time being, the last definitive mention seems to be the legal notice placed in the "Van Nuys News" in the Spring of '69:
"Van Nuys News", 6th April, 1969.