A little more on chassis with copper panels, Top Boost controls integrated in the panel, picking up from the main page on Expanded Frequency AC30s.

Below, an advert placed in the music press by Jennings on October 12th, 1963 - this appears to be the earliest mention in official JMI sources of an AC30 Twin with Top Boost. Super Twins with Boost controls on their back panels had been advertised as far back as September 1961. Was the Top Boost on the Twin listed in the advert below integral to its control panel, or a separate unit on the back?

12th October, 1963. The advert was repeated in early 1964.

The former is certainly possible. In late 1964, a Top Boost assembly, bought separately, cost £15 and 15 shillings. The Twin with Top Boost in the shop is pitched, on the face of things, at £26 and 5 shillings more than a plain Twin. A mistake perhaps, simply repeating the price given for the Super Twin?

In the pricelist issued in February 1964, the price given for a Twin with Top Boost is £131 and 15 shillings (= price of a standard Twin + £15 and 15 shillings).

JMI pricelist, February 1964.

Date codes

In all instances where the detail can be made out, the main preamp filter cap of early Top Boost chassis has the date code "UG" = July 1963. The span currently known is from serial number 10471 through to 3072, a Super Twin.

Detail of serial number 10672.

A chassis now without a box (and therefore lacking a serial number) has a 220K wirewound resistor with "UH" = August 1963. Its cathode resistor, along with those of at least two other amps, is 50R - and its GZ34 rectifier valve is dated 2nd week of November, 1963.

Jim Elyea supposed that (substantially) more than 500 copper-panelled AC30s with integrated Top Boost had been made. This is well over the mark. Certainly there are the Expanded Frequency amps, serial numbers 500-550, but then every sixth or seventh AC30 Twin in the range 10000-13000, and 2500-3100 for Super Twins? The actual figure is probably somewhere around 200-300.

The lowest serial number encountered so far for an amp with Top Boost controls integrated in a copper panel is 10348, which has Haddon rather than Albion transformers, and original components with June and July 1963 date codes. But 10348, as it stands, is unlikely to have been readied for sale before early '64. Its chassis is signed in pencil "DP" (the initials of the checker/inspector), "X" (for "Expanded Frequency"), "64" = 1964. It is certainly possible though that a small batch of chassis arrived at Dartford Road in September.

Most copper panel chassis with integral Top Boost controls are marked "DP" and "X" in pencil. This is the only one at present to have been inscribed with "64".

NOTE - It is possible that serial number 9029, a Super Twin amplifier section, is one of the very first copper panels with integrated Top Boost (to be substantiated).

NOTE 2 - Many chassis, presumably removed mainly from unwanted Expanded Frequency cabinets, have been "re-purposed" over the years - i.e. slipped into much later AC30 Twin cabs and so on (in one instance, a trapezoid AC30 Super Twin amplifier cab). Often, the holes on the upper edges of the back panels of these cabs do not align with the fixing points on the rear edges of the chassis.

NOTE 3 - Repro panels have been available for some years now so caution is needed.

Known surviving examples (as at February 2025)

The details given below are simply provisional - the picture as it stands at the moment. Further chassis and amps will doubtless come to light, the most recent to date being on ebay uk in early October 2023. One thing to be aware of is that dealers and enthusiasts have over the years made up saleable AC30s from unrelated parts - the chassis from one amp, the box (cabinet) of another, and so on. This still goes on. Two of the Super Twins and one of the Twins noted below are designated "Normal" voicing rather than "Top Boost" on their serial number plates.

EXPANDED FREQUENCY

Serial numbers: 10459, 10491, 10672, 11586, 11913.

Serial numbers: 505, 549.

Serial numbers unknown: 12 amps.

Remember that serial numbers 500-550, early in the sequence introduced for Expanded Frequency AC30s during the course of 1964, are all likely to have had copper panels.

SUPER TWINS

Serial numbers: 9029 (?); 10346; 10753 ("N" on plate); 12897 ("N" on plate).

Serial numbers: 2573 ("TB" on plate); 2583 ("TB" on plate); 2592 ("TB" on plate); 2690 (no voicing designated); 3072 ("TB" on plate).

Serial numbers unknown: 7 amps. No component date codes known for any of these at present.

TWINS

Serial numbers: 9158; 10348 ("TB" on plate); 10405 ("N" on plate); 12569 ("N" on plate); 12397; 12588 ("TB" on plate); 13532 ("T" on plate); 15417 ("B" on plate); 15621 ("T" on plate?); 19283 ("T" on plate).

The amps noted above with numbers in the 13000s and later are likely to be assemblages, created post JMI. Some of the others are likely to be also.

Serial numbers unknown: 7 amps. No component date codes known for any of these at present.

Photos indicate that by the end of February 1964 The Shadows had three. By April 1964 the Rolling Stones had two.

LOOSE CHASSIS

Serial numbers unknown: 8 chassis. Two of these have components with June and July 1963 date codes. One apparently has its original Mullard GZ34, dated 2nd week November 1963.

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