Small box, 2 channel amps; brown grille cloth; grey panel
Possibly 60-80 amps issued in this format?
The schematic for the valve rectified two channel AC50 is OS/053. See this page for a copy.
Effectively the brilliant channel followed the arrangement of the single channel of the earlier two input circuit (OS/044), but with two small changes - simply the modification of the values of two capacitors.
Above, a detail from the Vox "Precision in Sound" news flyer of late 1964. Note that the two channel AC50 for guitar is in a small box, and the AC50 for bass - the Foundation Bass - is large box.
Small box amps were made and issued side-by-side with large box probably for a couple of months, if not more. It is also evident that single channel amps were made and sold during this period. See the amps at the foot of the previous page.
Valve rectified AC50s were superceded in very late 1964 / early 1965 by solid state rectified amps - on this page. The schematic for the latter is OS/072.
Besides the obvious changes to the older type of chassis, one finds in the new valve rectified twin channel amps:
that the mains filter capacitors (behind the main power valves on the upper chassis) are now axial rather than vertical/radial;
the main internal fuse in the preamp is orientated upwards rather than longways;
there is now a single bias pot (new in circuit);
and the voltage selector is sometimes link, sometimes the newer plastic domed type.
Below, pictures of surviving amps, arranged by serial number - simply for convenience. Numbers were assigned fairly randomly to these amps by Triumph Electronics, which made them under contract for Vox.
Triumph employees often signed the underchassis of amps in pencil. DE = Dave Earp. RW = Roger White. Both Dave and Roger signed serial no. 1449, below.
Relatively few amps were issued in this format. At first it may simply have been a means of using up empty small boxes. But whatever the true impulse, safe to say that the twin channel AC50 amp inside the small box was exactly the same as the twin channel AC50 that went into the large box, the latter being the format that eventually predominated.
Serial number 1429 - currently in the USA
Sold on ebay in 2006. Brown grille cloth; white warning plaque; and what look like the original connectors. Input jack sockets are all black. A white pair for the "normal" channel seems to have been reserved for early large box AC50s.
Serial number 1436 - currently in the USA
With an AC30 cab. Amphenol "doughnut"-style mains connector; single rectangular Cannon output socket. Warning plaque centred. "13" chalked on the back board. Pot codes are "GL" and "HL" = July and August 1964.
Probably the same amp as above
Sold on ebay in 2006. Note the pattern of damage to the serial number plate.
Serial number 1449 - currently in the USA
Brown grille cloth, grey panel, domed voltage selector. Single speaker output. Note the "20" chalked inside the box and on the back board. A nice amp.
Serial number 1485 - currently in the UK
Grille cloth of both amp and cab originally black, but now faded. Note that the cab is of the later type with "handles" let in the side. We pass over the amp's handle in silence.
Serial number unknown
Only a shot of the front of the amp. Grille cloth renewed (Rose Morris pattern).
Serial number indecipherable - currently in the USA?
Two Bulgin sockets on the back panel. Domed voltage selector. No shots of the insides unfortunately.
Serial number unknown - currently in the UK?
Black grille cloth. A replaced mains transformer, but otherwise not in bad shape. "5" chalked inside the box and on the back board.
Serial number 1506 - currently in the UK
Sold on ebay. Replaced mains transformer and choke. Condition otherwise good.
Serial number 1524 - currently in the UK
Sold on ebay in 2011. Brown cloth, grey panel. Triumph-made, as all the AC50s pictured on this page - note the highly twisted leads from the transformers. Original connectors on the back panel.
Sold on ebay again in late 2013.