The Vox MC50
50 watt Public Address amplifier
The "MC" of the model name stands for "metal clad". MC50s (sometimes called the PA50) were produced for Vox under contract by Triumph Electronics in Purley along with the other models in the range - the MC15, MC30 and MC100. Triumph also produced AC50s for guitar and bass through to early 1965.
The earliest units, ie. those illustrated below, had plain metal cases with sloping fronts. Bulgin chicken-head knobs were fitted to the control pots. Initially all models had four channels: - three for microphone and one for music. Each had its own volume. Overall treble and bass could be varied via the controls on the upper right hand side of the fascia.
The power sections of the surviving units below are all solid state rectified. But it may be that the earliest units had valve rectification. It seems likely that the smaller metal-clad amps - the MC15 and MC30 - were valve rectified through to the end of 1965. No circuit diagrams for the MC15 and MC30 have so far come to light however. On the MC30, see this page.
In mid 1965, that is to say shortly before the range of public address amplifiers was expanded and revised, a certain number of four-input MC50s may have been produced with flat metal fronts rather than sloping. At least one four-input MC100 of this type is known.
One of the consequences of the expansion of the PA range in late 1964 / early 1965 was that the existing MC50 with four inputs became the MC50/4 to differentiate it from the new model with six, the MC50/6. The two versions of the MC100 were distinguished in the same way. In company with the MC100/6, the MC50/6 had a transistor preamp and valve power section. More on this page.
A detail from the JMI pricelist of November 1965.
By 1966, the PA amplifiers had blue-grey fascias and larger rectangular metal cases. See the examples on this page.
At least two JMI circuit diagrams (schematics) survive for the MC50 - SSC/004, which is probably early, and 0S/127, which is likely to be later. Copies of these will be posted when they are to hand.
In terms of electronics, from mid 1965 (and possibly before) the MC50 and AC50 mark 3 (solid state rectified, circuit diagram OS/072, drawn by Albert Hogben, and dated 7th January 1965) shared the same power section. There are a few minor differences, but they are otherwise identical. The preamp of the MC50 on the other hand followed that of the MC15, MC30 and MC100. The front ends of the Metal Clads were modular.
Presumably prior to January 1965, MC50s were valve rectified (matching the AC50 mark 2) - unless of course the design process was the other way round: the MC50 solid state rectified from the outset and the AC50 later adjusted to follow. But that is only a fairly remote possibility.
Serial numbers of the Metal-Clad public address amplifiers ran as part of the same series as the guitar/bass amps.
Although reasonably large numbers were produced, survivals are fairly few and far between, as is the case with most early public address amplifiers. Many are likely to have been gutted for parts or junked in the 1970s and 1980s.
References to PA units in music paper small ads have been collected together provisionally on the Vox AC50 website - on this page. A more substantial collection is in preparation.
1964
First generation Metal-Clad amplifiers
The sloping-front MC50 (MC50/4)
A detail from the catalogue of 1964, put to press in February 1964. Note that the units as described (though not depicted) have "two low impedance inputs" and a "master volume". Envisaged use: "For factory, theatre, club, pop groups, etc.".
The MC50/4 in the JMI pricelist of early 1964 - compiled in advance of the Frankfurt Trade Fair. The MC50/6 had not been brought into being at this point.
A detail from the "Precision in Sound" newspaper of 1964. The units pictured above have "three high impedance inputs and one music input" The surviving amplifiers below follow the format depicted.
Late 1964 to 1965
Second generation Metal-Clad amplifiers
The MC50/4 and the new MC50/6.
A detail from the Vox catalogue of 1965. The sloping-front MC50/4 and the new part solid-state MC50/6.
Vox MC50 (Metal Clad 50) serial number 2666
In superb condition. One of the blue Hunts capacitors in the power section has the date code "TDT"" = 48th week of 1964. The amplifier is likely to have been assembled at some point towards the end of the first third of 1965.
Vox MC50 serial number 3901
Sloping front, solid state rectified, assembled by Triumph Electronics for Vox in early 1965. Serial numbers ran in the same sequence as those assigned to AC50 guitar and bass amplifiers. Judging by small ads placed in music papers of the later 60s and early 70s, Triumph made reasonably large quantities of these Public Address units. They are scarce today however. Thanks to Daniel for the pictures.
Note the all valve preamp and power amp. Triumph also produced hybrid Public Address amplifiers for Vox - transistor preamp and valve power amp - long before the company embarked on making the 7-series range.
Vox MC50 serial number unknown
Sold on ebay some time ago. Well used, but all important components still in place.
On to the page on Vox PA50s, 1966 to 1968.
Back to the main index page on Vox Public Address equipment.