Accounts of the creation of the AC30 Twin - the twin-speaker version of the AC30 we all know and love - often begin with one of two things: an anachronistic graphic showing two AC15s and a split-front AC30 - "AC15 + AC15 = AC30"; or a story of some sort.

The stories are interesting, coming as they do from people close to "source". But there are puzzles, quite substantial ones: - sizeable gaps in the narrative, and evident contradictions, all to be expected perhaps of recollections decades after the event or events in questions.

Below, a brief synopsis of the principal stories together with brief notes and some key facts.

(1) Both Hank Marvin and Bruce Welch are clear that The Shadows asked Dick Denney for a bigger, louder amplifier (bigger and louder than the AC15).

(2) In an interview in "Guitarist Magazine" (October 2017) Hank related:

“I spoke to Dick Denney and asked him if it was possible to make the amps twice as loud; I said, ‘Can’t you put two of these together?’ and he said, ‘It doesn’t quite work like that!’ He went off and a little while later we had a call saying that he’d designed this new amplifier, an AC30, which was quite a lot louder than the AC15. So they knocked us up a couple and we started using those.”

(3) Rodney Angell, in an inverview for the "Vox Pop: How Dartford Powered The British Beat Boom" programme, broadcast on BBC 4 (30th January, 2012), stated that Dick asked Tom about making a new amp with two speakers. Tom said "No, No, No. Too heavy, too loud". [At this point the narrator comes in and says that Dick went ahead and made some anyway "...just to help out bands like The Shadows"]. Tom found out - spotting some [presumably tell-tale] items that Dick had ordered - and a huge row ensued. The upshot was that Dick was allowed to make 10 as a sort of trial - "on his head be it". Rodney worked for JMI first as an amp tester, then as a Research and Design engineer.

(4) Mike Ameson of MAJ Electronics recalls servicing TV Front AC30 Twins that had two output transformers (one for each pair of EL84s).

(5) The circuit diagrams for the AC30/4 and AC30/6 - single output transformers envisaged for both models - are dated 29th April 1960. The first adverts for the AC30 Twin were issued in Spring 1960.

(6) From summer 1960 to late 1960 The Shadows used two-tone AC15s (second circuit). JMI provided the band with TV Front AC30 Twins shortly before Cliff Richard's third season of shows on ATV, December 1960.

The chief difficulty in all this (as it has always been) is making sense of the recollections in relation to known facts.

One possible picture of events is that Dick actually did make some amps very early on - in February/March 1960, say, without Tom's knowledge. These had doubled-up output transformers. Two of the amps quietly assembled by Dick were given to The Shadows, but the band did not like them and did not use them publicly, later deciding to move to new two-tone AC15s (second circuit).

Tom and Dick had their row, and following that a first run of ten redesigned AC30 Twins was agreed. These were advertised in April 1960 (see the piece at the head of this page). Thereafter production proper hegan. In late 1960, some way into production, The Shadows were issued with a set of three TV Front Twins in time for Cliff's television shows. The amps would be seen by millions of viewers.

That perhaps is all well and good as far as it goes. However:

(7) Derek Underdown (quoted by Jim Elyea, p. 379) recalls that the move to design the Twin came not from The Shadows, but dissatisfaction on his part and Dick's with the single speaker AC/30. As the process of design continued, it was Derek's idea - not Dick's or Hank's or anyone else's - to "double up" the EL84s to form the AC30. Jim suggests (p. 379) that the design process began in late 1959. Possible. The quotes from Reg Clark (pp. 379-380) tend to suggest early 1960 though.

(8) Throwing a spanner into the works of those who have assumed that the AC15 alone was used as a base point, Derek recalls "I believe that Dick liked the output stage shown in the Wurlitzer organ data..." It is perhaps worth noting that most Wurlitzer organs in the 1950s and early 1960s - the Spinette Model 44 and later derivatives - used 6L6 power valves. Hammond and Baldwin did employ EL84s though (6BQ5 being the American designation), as did the Wurlizter "Sideman", a primitive drum machine.

(9) Much the same "division of labour" prevailed also for the design of the AC50 and AC80/100 later on. Derek Underdown oversaw the power section, Dick Denney the preamp, though both naturally had a say in each other's work. Alan Harding, Derek's principal assisant in practical R&D matters, probably had some hand too.

Below, what may be a chassis assembled during the process of prototyping. It is not all plain sailing though. More questions than answers surround it.

As for the AC30/6 chassis embodied in the TV Front Twin with serial number plate 4290 added to its backboard, all bets are off. Unfortunately many of the early amps have been subject to numbers of "changes".

A prototype?

Notes on the design of the AC30 Twin and on the "prototype" chassis published by Jim Elyea (p. 381) .For the time being, notes and questions only.

Valves are 2 x EL34, four double triodes (ECC82/ECC83); and one taller valve or at least a taller valve shroud.

All the weight of transformers and choke is at one end. This is countered, though only to a small degree, by the off-set preamp upright. Preamp uprights and valves do not weigh much.

The preamp has one control for "Tremolo", three channels (a volume control for each), and Bass and Treble tone controls.

Why are there four inputs in a diamond arrangement? The only other amp in JMI's catalogue to have had such an arrangement was the second version of the AC50 Mark 1 (mid 1964), produced by Triumph Electronics - see below.

Does the amp only have "Tremolo", not "Vibrato" too?

Does any amp produced by JMI have "Presence" to describe "Tone" controls? Most if not all have "Tone".

The three valves on the preamp "chassis" extend through holes the plinth underneath. Extremely eccentric.

The preamp is "free-wired" - there is no tag board.

The insulated connection spurs / stand-offs in the preamp and on the plinth are typical of Triumnph Electronics, not JMI.

The signal from the preamp is taken to the power section (on the underside of the plinth) via a spur on the top of the plinth, not via a pass-through hole.

A detail of the preamp, the spurs / stand-offs indicated with arrows.

What if this were a design - or at least a first attempt at a design - produced by Triumph Electronics for Derek and Dick? Triumph did a good of contract work for JMI throughout the 1960s. The only date code visible is on the tall TCC 16+16uf capacitor - "QC" = March 1959, which is naturally the date of the capacitor's manufacture, not the amp's.

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