All units manufactured by Hylight Electronics from 1966 to 1981 had a serial number plate like the ones in the pictures below attached to the metal chassis of the amplifier.
All of these plates bear the marking All units manufactured by Hiwatt Biacrown from late 1981 to 1984 had a serial number plate like the one in the picture below attached to the metal chassis of the amplifier.
The preamp of the AC50, essentially a reworking the top boost circuitry of the AC30, was created in-house by Denney himself. Above, a detail of the tone circuit of the AC50, and below it, the top-boost circuit of the AC30, designed in 1961 ("borrowed" by Vox from the Gibson GA-70).
The power amp, employing a valve rectifier (a GZ34) and two EL34s operating with fixed bias was probably designed at JMI, with input from Triumph Electronics.
The design process evidently began in the summer of 1963, and was well advanced, if not complete, by August 1963, as an advert published the issue of "Beat Monthly" attests. Note the mention in the advert of "separate amplifier cabinet provides a total output of 50 watts undistorted", indicating that the AC50 was ready or close to being ready.
Although the first schematic for the new amp - OS/044 - bears no date, it seems reasonable to assume that the circuit was pretty much settled by late September.
Amplifiers with a serial starting with a single letter and bearing a plate which has "HIWATT UK" and LONDON or DONCASTER on it were made starting in the early 2000s by the current Hiwatt manufacturers, Music Ground.
Options: VFS2A Footswitch VOX AC30C2X Custom Specifications Output Power: 30 Watts RMS into 16 Ohms Speaker: 2 x 12" 8 ohm Celestion Alnico Blue Inputs: Normal input jack (high and low), Top Boost input jack (high and low), FX RETURN jack, Footswitch jack Outputs: External loudspeaker jack, Extension loudspeaker jack, FX SEND jack Dimensions (W x D x H): 702 x 265 x 556 mm / 27.64 x 10.43 x 21.89 inches Weight: 33.4 kg / 73.59 lbs.
Options: VFS2A Footswitch *Specifications and features are subject to change without notice.
Design The AC50 was brought into being initially with one end in mind: supplying The Beatles with power enough to make themselves heard over legions of screaming fans.
John and George were to have 50 watt amps (the AC50), and Paul an 80 watt bass unit - the AC80/100, later the Vox AC100.