Vox PA units

1964 - 1967

From mid 1964 - 1967 Triumph Electronics produced a series of PA units for Vox - designated "Metal Clads" (MC) as the boxes were metal (in contrast to the wooden cabinets of Vox guitar amps). Both in terms of construction and sound these PA amps were naturally very different from the AC50s and AC100s. Without modification, they are not particularly well suited for guitar and bass - the Mic channels are too sensitive, and the Music channel too low gain. But for their intended purpose, the PA amps pack a mean punch, and they will clearly have done the job in clubs and smaller halls - added to that, they are beautifully constructed internally.

For more on Triumph Electronics. Triumph also assembled AC50s for Vox from 1964 - 1965. A selection of amps can be viewed on the Vox AC50 website.

A page from "Beacon", July 1967, the Journal of the Royston Group of Companies - the group that owned JMI. Pictured is Cyril Windiate, secretary to Tom Jennings. The piece extols the virtues of a PA system set up by Vox.

On the right, a page from an illustrated Vox catalogue, 1965. Right, Dick Denney with an early flat-fronted PA in 1964 at the Russell Hotel, its Vox logo highly drawn out. The unit on top is a "Page-Boy" office PA mixer.

Vox PA units

Below a sloping front MC50 from 1965. Note the standard AC50 serial number plate (ie. no designation that the amp is a PA). Caution is needed though, as Triumph used such plates in a completely unsystematic way.

Serial number 2666 - currently in the Netherlands

For further pictures of this fine amp, see the on which the images were originally posted.

Serial number unknown - currently in the UK

A set of small images from 2005. Transformers (and choke) differently appointed from the example above.

In 1965 The Who evidently used a similar unit, but theirs was probably a 100 watter:

On the left, the PA amp behind John Entwistle. On the right, a page from the 1965 Vox catalogue (repeated from above).

Pictures of surviving early 100W Vox public address amplifiers are yet to materialise.

Vox PA units

In 1966 Triumph Electronics put into production for Vox a new set of 50W and 100W public address amplifiers, some with transistor preamps, though the power sections remained all valve. The blue/grey and white livery was applied also to the growing array of , and other devices:.

Above, the Vox Guitar Organ power unit

In terms of electronics, a notable feature of the new 100W PA amps is the provision of individual bias controls for the output valves, similar to those of the Vox UL 4120 and UL 7120, also assembled (and designed) by Triumph.

The PA50s retained their standard AC50 serial number plates.

Speaker outputs were either 1/4" jacks or, unusually, large Bulgin two-pin bakelite sockets. Triumph sourced its transformers for these amps from Drake.

Vox PA units

PA50 type 2 - transistor preamp, meter on the front

Serial number unknown - currently in the USA?

Whereabouts unknown.

Serial number 7597 - currently in Spain

A beautiful metered PA50 - serial number 7597. Presumably, as in the PA100 immediately below, a transistor preamp. Power section 2 x EL34 with individual bias.

PA50 type 3 - all valve, no meter, redesigned box

Serial number unknown - currently in the UK

A metal-clad 50 watt version of the 100W amps below. The preamp valves date to 1965. However, one of the pots has the code LN = December 1966; and another FN = June 1966; so the amp was probably produced for Vox early in 1967 by the Triumph works. A few repairs here and there, and fairly scuffed on the outside, but otherwise in good condition. The transformers appear to have been made by Drake and have codes that will be familiar to those who know Marshall amps: output transformer is 784-125; power transformer is 1202-112A and the choke 352-169. From the sticker on the front, the amp seems to have been used somewhere in Northern Ireland.

Serial number unknown - currently in the UK

Sold on ebay.uk in October 2013 - not in working order, but easy enough to remedy. Note the three-line serial number plate. The number is at present unknown.

Serial number unknown - currently in Australia

Rear panel arranged slightly differently from the two PA50 amps pictured above. To judge by the position of the EL34s, the internal chassis must be fairly low.

Vox PA units

PA100 type 2 - transistor preamp, meter on front, two speaker outlets

Serial number unknown - currently in the UK

Currently in the UK, an extremely rare PA 100 with power meter. The transistor preamp looks good and intact; the power section does require a little attention though. Two of the four EL34s were replaced at some point by 6L6s.

June 2013 - the amp now beautifully restored and in full working order. Thanks to Mick for the pictures.

PA100 type 3 - transistor preamp, meter on front, four speaker outlets


Serial number unknown - currently in the UK

Sold on ebay in September 2014. Box and power meter missing, but great condition. Assembled by Vox for Triumph Electronics. The preamp, as above and below, is solid state. Power section is all valve with individual bias controls for the EL34s.

Serial number unknown - currently in the UK

Sold on ebay.uk in early 2014. Just the power amp chassis, but in good condition. This is a larger (wider) unit, as above, with four 1/4" jack outputs rather than paired round Bulgins.

PA100 type 4 - valve preamp and power amp, redesigned box, two outputs

On the left, the band Styler's Musical Express playing at the Lion Hotel, Singapore - note on the centre of the riser a metal-clad PA much as the 100 watter below. Centre and right, the Yardbirds, April 13th, 1967.

Serial number unknown - currently in the UK

A 1966/67 monster in good physical and cosmetic condition. Many elements are similar to the 7-series amps - tagboards with eyelets (instead of hooks), Mustard capacitors, insulated stand-offs on the chassis, and individual controls for the output valves' bias on the back panel. The EL34s are the original ones, with Mullard date codes B5G2 = Blackburn Factory, 1965, 2nd week July.

Vox PA units

Later, it seems that there was a plan to replace these amps with a new all solid state version, as part of the line of all solid state guitar amps (the Conqueror, Defiant, Supreme, and so on):

Image from a brochure reproduced by J. Elyea, Vox Amplifiers. No surviving examples have hitherto been seen however.

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