Vox PA units

1964 - 1967

From early 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. An extensive series of amps can be viewed on the .

For the 100 watt Vox public address amps and further notes on chronology, .

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.

Dick Denney with a new six input flat-fronted PA in 1964 at the Russell Hotel Trade Fair The unit on top is a "Page-Boy" office PA mixer.

A detail from a catalogue of 1965

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 JMI added plates to Triumph-made amps in a rather unstructured way.

Note that all the amps below are solid state rectified, a form of circuit introduced in early 1965.

Serial number 2666 - currently in the Netherlands

For further pictures of this 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.

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:.

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.

PA50 six input - transistor preamp

Meter on the front

Serial number unknown - currently in the USA?

Whereabouts unknown.

Serial number 7597 - currently in Spain

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

PA50 four input - 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.

23rd April 2017. Further pictures of the amp showing the chassis and electronics. Thanks to Will. Note the valve sockets, supported on brackets at a level lower than the rest of the chassis, presumably to obtain as much headroom for the EL34s as possible. A similar solution was applied to the Beatles' 7120 amps, also made by Triumph. The output transformer of this PA, which provides a 100V line for hall or field speakers, is absolutely massive. No maker's stamp is visible on the OT and PT, but they may be Wodens. Note on the underside of the latter the varnished/waxed cloth wrapping - identical to the wrappings in the Woden transformers in AC30s, AC80/100s and so on.

Just to note, the choke certainly is Woden. There is no date code (unusual for Woden), simply the PA model number - MC/50/3, ie. a Vox MC50 mark 3.

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