VOX SOLID STATE PUBLIC ADDRESS (PA) EQUIPMENT
Vox Sound Equipment Ltd, and Vox Sound Ltd - 1969-1973
The 50W and 100W Public Address amps originally advertised by Jennings Musical Industries in April 1967 with the rest of the solid state line, seem not to have appeared. No surviving example has come down to us at any rate.
Above, the units presented in the catalogue.
For the better part of 1967 and 1968, the PAs available for purchase will presumably have been the ones assembled by Triumph before it ceased contracting for JMI (in late '67). Triumph produced a variety of units, some fully solid state, others all valve. A proportion were "hybrid". For the 50W amps, see this page on the Vox AC100 site. The 100W amps are here.
The Vox PA50SS and PA100SS
The first new solid state units produced by Vox in actual fact were the ones pictured below, exhibited at the Frankfurt Musikmesse in March '68 and later at the British Musical Instrument Trade Fair in August - the Vox PA50SS and 100SS, sometimes known also as the SS PA50 and SS PA100:
The Vox display at the Frankfurth Musikmesse, March 1968. In terms of appearance, not a particularly scintillating presentation, alas (at least insofar as this shot records). In the background, the new solid state PA amps - the 50SS and 100SS - which are mentioned also in Gary Hurst's report of the British Musical Instrument show in August:
Excerpt from Gary Hurst's review of the Russell Hotel show, Aug. 1968.
In terms of functionality, the PA50SS had four channels - one for music, three for mics; and the PA100SS six - one for music, five for mics. Each channel had its own volume, bass and treble controls. A master volume governed overall levels.
The mains socket was a Belling Lee L1722, standard across the Vox solid state range. All the amps have four selectable output loads: 4, 8, and 16ohms, and 100V line voltage for field or hall speakers.
The chassis of the PA100SS, which slides out of the front of the box when the retaining screws are removed, was fully rack-mountable: 19 inches wide, 5.25 inches (3U) tall.
The circuits incorporated in the PA50SS and 100SS differed from the guitar and bass amps in the solid state range in two major respects: they not only included an impedance matching "output" transformer, but had a limiter circuit to prevent clipping (distortion).
It is worth noting however that the power sections were still based around the 2N3055 transistor, a real workhorse in the solid state world. Two reasonable good schematics are posted below.
PAR100SS. Pictures of a late example are available here. Development of the PAR100SS took place towards the end of the VSEL period (ie. in late 1969). Reverb could be assigned individually to all six channels, activated by a push-pull volume control. A master volume governed its overall level. The effect could be switched in and out via a footswitch. The chassis, which was also used for the Midas Reverb, is deeper than that of the PA100SS to accomodate the reverb tray.
Trays took the same form as those used in the solid state guitar amps - the Conqueror, Defiant and Supreme - a single spring with Sontone phono cartridges as transducers. The schematic for the PAR100SS is OS/214. Reverb was never provided for the PA50SS.
The Vox Sound Equipment Limited schematic for the PA100SS mark 1 is OS/176; the PA50SS is OS/177.
OS/176. Click for a larger version. Enlarge further by clicking on the symbol that appears lower right. A good complete copy of the schematic, including the schedules of changes at top left.
OS/177 for the PA50 SS. The earliest visible change at top left is 2th November 1968 (though another clearly preceded it).
Vox Sound Ltd evidently used existing VSEL sheets. One can see in the snippet below, that the "Equipment" of "Vox Sound Equipment Ltd" has been erased to leave "Vox Sound Ltd".
Small section of OS/176 for the Vox SS PA100.
The same emendation can be seen in the schematic for the PAR100SS (ie. the model with reverb), changed from VSEL to VSL.
Small section of OS/214 for the Vox SS PAR100. The first noted change to the circuit on this schematic is 10th July 1970.
Below, a register of surviving amps. If anyone knows of solid state Vox PAs that have not yet been included, do let me know.
The Vox PA50SS - Public Address amplifier
50w, solid state, four channels
Above, the (incomplete) section of the "Vox Sound Equipment Limited" schematic for the PA50SS, top left, noting changes and dates, the first visible entry being for November 1968 and running through to July 1970, which corresponds with the beginning of "Vox Sound Limited". On VSL, see this page.
Vox Sound Equipment Limited. Note the wire grille on the underside. The string round the box is silver.
Vox Sound Limited. Plastic vents now top and bottom. Serial number 1310.
The Vox PA100SS - Public Address amplifier
100w, solid state, six channels
Above, the section of the "Vox Sound Equipment Limited" schematic, top left, noting changes and dates, the first being February 1969 runing through to July 1970, when Vox Sound Limited took over production.
Vox Sound Equipment Limited. Serial number 1117. Note the wire mesh grille on the underside - also used for the early PA50SS a little way up this page. The string round the box is silver.
Vox Sound Limited. Serial number 1267.
Vox PAR100SS - Public Address amplifier
100w, solid state, six channels, reverb
The PAR100SS was designed by "Vox Sound Equipment Limited" - in late 1969 or early 1970. Available copies of the schematic - OS/214 - are a little smudgy. The detail above is from the top left corner. The first entry is for 1970 (month unreadable), with a second of July 1970 (also the PA50SS and PA100SS). For details of a PAR100SS from mid or late 1972, see this page.
Vox Sound Limited. Serial number 1006. Note that the full name is given in the plate: "PA 100 SS REV". Further info to follow.
Vox Sound Limited. Serial number 1013. Thanks to Jim for the pictures.
Serial number 1057. The red CCL bias caps bear the date "OCT. 70", so this amp was probably produced in early 1971. Date codes of other components to follow.
Vox Sound Ltd. Serial number 1245.
Vox Sound Ltd. Serial number 127x.
Vox Sound Ltd. Serial number 1440. A new style of serial number plate.
Vox Sound Ltd. Serial number 1497.
Vox Sound Ltd. Serial number 1521. Style of serial number plate as number 1440, above.
For the Vox Midas amplifier, now see this page.