Amps assembled at the Burndept factory (always the presence of the stamped chassis number). American-style logos.
The band "influention" with a late large box AC50 (note the logo) on top of a Super Foundation Bass speaker cabinet.
The external characteristics of these amps are much as serial numbers 7400-7999: American style logo at front, two-pin corner protectors, Amphenol connectors on the back panel. The only major difference is the regular appearance now of the white warning plaque.
Internally: amps begin to have more and more components used in the solid state amps: yellow Dubillier coupling caps in the preamp, and small Radiospares potentiometers. CCL capacitors had already been brought in by around serial number 7400.
It is also worth noting that cathode bypass caps are dropped for the preamp valves (V1 and V2).
Above details from serial no. 8168. First pic showing one of the small pots in the preamp (the same type as in the early solid state amps). The second pic showing two of the yellow Dubillier caps. For examples of the Vox solid state amps, see for instance this page.
By serial number 8168, however, we are already well into 1968: the CCL filter capacitors are dated "B8" = February 1968. An outline of the CCL codes is given here.
In the left-hand capacitor, one can only see the name "CCL". At right though, we have the date code "B8".
These late amps were produced close to the end of Jennings Musical Industries (in mid 1968). For the rise of "Vox Sound Equipment Limited" (VSEL), which took over from JMI, see this page on the Vox Supreme website. AC50s issued by "Vox Sound Equipment Limited" are registered here.
Below, a register of amps. If anyone knows of others that have not yet been included, as ever do let me know.