Below pages from the Mullard "Audio Valves" booklet of April 1954 relating to the ECC83 double triode - specifications and characteristic curves. As is well known, AC30/6s used four:

V1: one half each for the Normal and Brilliant channel input stage.

V2: Phase inverter.

V7: Brilliant channel input, and first Vib/Trem stage.

V9: Vib/Trem circuit oscillator.

Detail of JMI circuit diagram OS/065 for the AC30/6, the circuit originally drawn up in April 1960. The two triodes of V1 (ECC83) are the inputs of the Normal and Brilliant channels. V2 (another ECC83) is the phase inverter.

Remember too that ECC83s were also used from late 1957 in the Jennings Vibravox unit ( see this page); in the preamp of the single speaker AC/30 of 1959-1960 (four in total); and in the preamp of the AC30/4 - V2 (Phase inverter), V5 (Vib/Trem input, and first gain stage); and V7 (Vib/Trem oscillator). V1 in the AC30/4 was of course an EF86.

From 1959 to mid 1962, Mullards were the norm. From late 1962 to 1965 one finds both Brimars and Mullards: the former normally fitted by Burndept, which started producing chassis for JMI in the autumn of 1962 (the Brimar factory was not far from the Burndept Works); the latter fitted by Westrex. In 1965 Westrex's contract came to an end. From 1965-1968 Burndept used both Brimar and Mullard.

Notes will be added shortly on the date codes of Brimar and Mullard valves.

Mullard's booklets were updated periodically to include details of new valves. In late 1954 the GZ34 was introduced, and in 1957-1958 production of the EL34 began at the Blackburn factory. JMI will have had multiple copies of the various issues.

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