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.

A detail of testing at the West Street Works in Spring 1967. At left, a PA50 chassis, two speaker sockets on its back panel. PA100s had four.

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 new solid state public address amplifiers were exhibited for the first time by Jennings (as the company still was) at the Frankurt Fair in March 1968. Later in the year they were displayed in a slightly revised form by "Vox Sound Equiment Limited" at the British Musical Instrument Trade Fair (August '68):

The Vox display at the Frankfurt Musikmesse, March 1968. In terms of appearance, not a particularly scintillating presentation, but JMI at the time was struggling, having been in the hands of the receiver since December 1967.

A detail from a rough-print picture published in the German music trade press, March 1968 - SSPA100 at left, SSPA50 to the right. Note that the cases are metal.

Excerpt from Gary Hurst's review of the Vox display at the Russell Hotel Trade Fair London, August 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 probably 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 Sonotone phono cartridges as transducers. The schematic for the PAR100SS is OS/214. Reverb was never provided for the PA50SS.

Schematics

The "Vox Sound Equipment Limited" schematic for the PA100SS mark 1 is OS/176; the PA50SS is OS/177.. A JMI sheet for the PA50SS survives in thr form of SSC-004.

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, drawn up in March 1968 (see the detail of the information panel, a little below). The image of the sheet has been slightly cropped at top. The original Works sheet measured 35 x 23 inches. The earliest change at top left is 2th November 1968.

SSC-004 - the JMI sheet for the circuit. Note the two types "SSG" and "SSP" - "Solid State General Purpose" and "Solid State PA" (?) In the circuit diagram an alternative transformer-based impedance-matching microphone input is represented for the "SSP", so it is likely that the distinction between the two types of amp was the type of microphone that could be used.

Additions aside, SSC/004 differs from OS/177 in four main respects. Certain parts are drawn differently (esp. at the output); signal voltages are not given; three of the printed circuit boards have JMI numbers: J.M.I./93 to J.M.I./95; and the layout sheets referenced are SSL/001 to SSL/003 instead of A222 and A241 in OS/177.

"Vox Sound Limited" 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 a copy of the original VSEL / VSL Works circuit diagram for the Vox SS PAR100 (OS/214). The first noted change to the circuit on this schematic is 10th July 1970.

Below, an overview 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, master volume

A new page (November 2025) on the PA50 - has now been started here, further material to be added.

Detail from the "Vox Sound Limited" catalogue of August 1971.

The Vox PA100SS - Public Address amplifier

100w, solid state, six channels, master volume

A new page (November 2025) on the PA100 - has now been started here, further material to be added shortly.

Detail from the "Vox Sound Limited" catalogue of August 1970.

The Vox PAR100SS - Public Address amplifier

100w, solid state, six channels, reverb, master volume

A new page (November 2025) on the PAR100 - the PA100 with Reverb - can be found here, further material to be added shortly.

Detail from the "Vox Sound Limited" catalogue of August 1971.

Serial number 1006

Note that the full name is given in the plate: "PA 100 SS REV".