A Vox MC100/4 from late 1964
Second version; flat front; silver grey finish
"MC" = "Metal Clad". External dimensions of the metal case: 16 3/4" long x 14" wide x 7 1/2" tall. Weight: around 56lbs (25kg). Pictures of the case can be found at the foot of this page.
General specifications: four channels, three for microphone, one for music, a volume control for each, overall treble and bass control. In the preamp four ECC83 valves; in the power section one ECC82 (phase inverter) and four EL34s with adjustable bias. 100 watt output into an 8 or 16 ohm load.
Early circuit diagrams for the model have not come to light so far. A later sheet survives in the form of OS/086, first drawn in the summer of 1965 and incorporating notes of further changes.
Serial number plates were glued - probably araldited - to the underside of the cabinets. None has survived on the amps that have so far come to light. Serial numbers will have been part of the main AC100 sequence. The amp pictured below is likely to have had a number in the high 100s / low 200s.
The earliest version of the MC100/4 had a sloping front and was still being promoted in late August 1964 (photographed at the Russell Hotel Trade Fair, pictures to be published soon).
The sections below: Preamp; Power section; and Case.
Preamp
Rear of preamp.
Pot code "DL" = April 1964.
Underside.
Mullard mustard capacitors with "A4N" and "C4N" date codes - respectively first and third quarters of 1964.
Side view. MC100/4 preamp assemblies were originally designed with the sloping front in mind (MC100/4 version 1) - which is why the rear is shorter.
Power section
The rear panel of the MC100/4 - standard terminal block (from factory) for speaker connections rather than the Belling Lee L1469 strips used on these amps from Spring 1965.
Rear panel.
Rear of the front panel showing the lines from the output transformer to the terminal block. Orange grommets are always a good sign of assembly by Triumph.
The amp below, similar in date to the one above and also in the UK, was evidently prepared in much the same way:
Transformers: these are massive open-frame units, probably made for JMI by Drake. The lamination stack of the mains unit for the MC100/4 measures: 5 1/4" x 4 1/4" x 3". The output transformer's stack measures: 5 1/4" x 4 1/4" x 2".
The designations on paper slips are "D45M/1" (mains) and "D55 O/1" (output). The choke is unmarked.
Upper chassis, power section.
Mains transformer sticker.
Output transformer sticker
A couple of shots of the underchassis power section of the MC100/4, electrolytics evidently replaced a few years ago. The bias network differs in a couple of respects from the one in the other MC100/4 with a discrete bias board.
The rectangular opening in the rear lip is for the bolt attaching the section to the metal case.
The date code on the Mullard mustards is "C4N" = third quarter of 1964.
Metal case
For the time being, a couple of general views. Further details will be added in due course. The black paint is old but probably not original. MC100/4 cases were normally finished in silver grey hammerite.
Underside, serial number plate probably long gone.
On to the page on Vox PA100s, 1966 to 1968.