The circuit diagrams on this page all come from hard copies - sometimes copies of copies - made numbers of decades ago. It seemed rather redundant to gather together copies of things that are currently in circulation in publications and on the web. The circuit for the AC30/4 will be provided on a separate page.

As for the sheets below, OA/025 and OS/065 are to all intents and purposes one and the same - "Works Use Only"; first drawn out on 29th April 1960; same list of additions and dates down the right-hand side; the final date 11th September 1964.

OA/026 was the sheet included in the Thomas Organ Service Manual of 1966, and seems also to have been the one more frequently sent out to service engineers in the United Kingdom. OS/065 was circulated in the UK too though.

Leaving aside their quirks, OA/026 and OS/065 have all the appearance of being master sheets, corrected and brought up to date by erasure and redrawing. The notes "ISS." suggest that at certain points other sheets - ISSUES - were produced for use outside the factory.

Clearly in 1962, OA/026 and OS/065 would not have changes relating to 1963. Surely somewhere there must be earlier versions/issues? Westrex and Burndept, the two principal contractors that assembled chassis for JMI, are likely to have had multiple copies along with their own wiring diagrams.

Note that no JMI sheet has come to light so far for the AC30/6 with integrated top boost (controls in panel).

Circuit diagrams of course are only part of the picture. Engineering drawings of various elements - transformers and so on - will also have been made. The company that printed the engineering drawings for "Vox Sound Limited" in its original incorporation (1970-1973), was "A. & F. Royal Limited" in Crawley, Sussex. It is not known at present who printed sheets for JMI.

Click on the images below for larger downloadable versions (3600 pixels wide).

JMI: 1960-1968.

[O]A/026

There are apparently two versions of this sheet. One is identical to OS/065, below. The other is dated 14th June 1963, which may mean either that it has additional entries up to this point, or that it is dated 14th June 1963 in the information panel and that all "modifications" have been silently incorporated in the diagram. The owner of this sheet will provide a description in due course.

Note that OS/010, the diagram for the add-on Top Boost unit, references OA/026, not OS/065.

OS/065 (also as OA/026)

AC30/6 Normal, with detail of "List of Changes" panel

Dated 29th April 1960 in the lower information panel. Drawn by Dick Denney (RD). Many changes (see below). The sheet is a copy of a copy, probably from "Modern Music" in Dudley. Values are good and legible, except in one instance, which has been supplied in red. Someone has added a potential negative feedback loop!

First change: 7th February 1960. Main "List of Changes": 8th May 1961. ISSUE 2: 14th June 1963. ISSUE 3: 11th October 1963. ISSUE 4: 11th September 1964, no changes marked, the entry made by Dick Denney. 11th Sept. 1964 is the date on or after which the modifications were incorporated in the main circuit (ie. in the main body of the diagram). Two of the additions were made by Mike Turner (MT).

OS/056

AC30/6 Treble

Dated 10th September 1964. Drawn by Dick Denney (DRD) and checked by him. The modifications noted on OS/065 are incorporated. Only a few divergences from the AC30/6 Normal circuit: C2, C3, C5, C6, C7, C9 and C10; the cathode circuit of V1; and at each of the three volume controls, a 330k resistor and 220pf (not numbered) to enhance the treble response further. This sheet was part of the Thomas Organ service manual for amplifiers first issued in the USA in 1966.

OS/057

AC30/6 Bass

Dated 11th September 1964. Drawn by Dick Denney (DRD) and checked by him. The modifications noted on OS/065 are incorporated. Only a few divergences from the AC30/6 Normal circuit, all capacitors: C2, C3, C5, C6, C7, C9 and C10. This sheet was part of the Thomas Organ service manual for amplifiers, as above.

OS/010.

AC30/6, add-on Top Boost unit, 1961

Dated 11th December 1961. Drawn by John Bell. Note that the sheet references [0]A/026, not OS/065. Issued as part of the Thomas Organ service manual for amplifiers.

A62-005

Reverb unit, 1962

Dated 30th January 1962. Drawn by John Bell.

OS/075

AC30/6, add-on Reverb unit, 1965

Dated 15th January 1965. Drawn by Albert Hogben. Circulated as part of the Thomas Organ service manual for amplifiers (as above).

OS/075/R

AC30/6, add-on Reverb unit, 1965

Dated 14 October 1965. Drawn by Albert Hogben. Changes to 26th January 1966. A simplified version of OS/075.

Vox Sound Equipment Limited: 1968-1969.

OS/013

AC30 Top Boost.

Dated 20th November 1969. Based on OS/065 (copied onto a larger sheet), the Top Boost circuitry added above it by draughtsman "PG".

The two pictures above from another copy, clearer in some respects, feinter in others. Note that in the top panel there is a large gap between "Sound" and "Limited". "Vox Sound Equipment Limited", the name of the previous company (1968-1969), originally stood there, "Equipment" having been erased. In the lowest but one panel, the hand-written "Vox Sound Ltd" may have been supplied over the erasure of "Vox Sound Equipment Limited".

The sheet was drawn by the person that drew the VSL diagram below. Its number - OS/013 - should on the face of things be a JMI number. OS/011 (redrawn in 1964) is for the JMI Reverb unit; OS/012 (dated 15/09/58) is for a "Jennings Organ Company" V-series organ power section. No JMI sheet numbered OS/013 is known. If OS/013 is not simply a mistake for OS/213, which would certainly be a VSL sheet, then it may be that VSEL or VSL simply used an unallocated number in the old sequence. There are quite a few gaps.

Sheet for Italian-made AC30s

The information panel.

The sheet as a whole.

Above, the circuit diagram for the AC30 drawn up in Italy by E.M.E - thanks to Michael. The date of the drawing is given as "17/11/68", On 28th Feb. 1972, the sheet was stamped and signed off. The circuit encompassed is the AC30 Top Boost.

E.M.E - Elettronica Musicale Europea - was the joint venture between Jennings, Thomas Organ, and Eko, set up in mid 1966 in a huge factory in Recanati (a little way south of Ancona), funded in part by the Italian government.

Vox Sound Limited: 1970-1973.

Sheet without a number

The compiler of the diagrams below had evidently been taught to write on the continent - the stem of the number "7" for instance has a cross stroke. Other continental traits are visible throughout.

AC30/6 Top Boost

Dated 12th February 1971. No information panel. A later addition has been made at the input of V1 (ECC83).

OS/249

Solid state AC30/6 with Reverb

Drawn 30th May 1972. Solid state amplifier. Changes through to 2nd February 1973.

Dallas Musical Industries: 1974.

SC/V/1313

AC30/6 Top Boost

Dated 24th June 1974. The sheet is an original intended for service engineers.

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