Celestion 18" bass speakers - 50W power handling
The earliest Vox Foundation Bass cabs had Goodmans Audiom 90s, the first heavy duty 18" driver made by a British company. As soon as Celestion ceramic units became available in early 1964, however, Vox adopted those - probably on the grounds of cost. The Goodmans Audiom 90, with its large alnico magnet, was fabulously expensive.
The Celestion speaker - the T1079 - was sprayed blue - the same blue used for the alnico T530s that went into AC30s.
The T1079 - sprayed blue
The speaker below has probably been reconed. The tell-tale signs are the brownness of the cone, and the rupturing of the Vox sticker to allow access to the hex nut underneath it.
The T1108 - sprayed silver (poly grey)
The Celestion T1108 is effectively the same speaker as the T1079, but sprayed silver, matching the new colour of the alnico 12" speakers - the T1088s - that went into AC30s. Since the silver (poly grey) T1088 was introduced in May 1964, it seems reasonable to think that the T1108 came in at this time too.
T1108s were used until late 1964 / early 1965. Thereafter Celestion adopted a new style of frame with four tapering struts instead of six scallop-shaped openings.