A Vox PA mixer - Mark 2, late 1964

Detail from OS/058, drawn out by Bert Hogben in October 1964, to show the information panel. The number is less cropped top left on the sheet.

Thanks to Martin, some preliminary shots of a Mark 2 Mixer Unit from late 1964. The circuit diagram is OS/058, dated October 1964. The Mark 1 and Mark 2 mixers were assembled for JMI in Bexleyheath. Around fifty are said to have been made with detachable fronts. The boxes were made by Glock, based in Crayford a couple of miles away.

The circuit for the Mark 1, which had a single tone control, was "borrowed" complete with original flaw from an existing Japanese unit. The JMI circuit diagram for the Mark 1 is likely to have had a number somewhere between OS/045 and OS/050, late 1963 / early 1964.

The unit pictured below is the only surviving example currently known of a Mark 1 or Mark 2. Some shots of the electronics to follow, along with details of the circuit diagram (OS/058). The main page on JMI's Mixer Units can be found here.

Mark 1 mixers had hinges at the top.

Underside

A quick comparison of the Mark 2 and Mark 3 mixers. The Mark 2 (without front cover) measures: 14" x 4 1/2" tall x 4" deep. The Metal Clad Mark 3 measures: 14" x 5 1/4" tall x 4 7/7" deep.

A page on the Metal Clad unit can be found here.