A glimpse of JMI's design process - the steps leading up to full production, in this case, of the T60. In November 1962, Jennings placed a short note in the music trade press to indicate that prototypes for the T60 were "well under way". It is probably no accident that the earliest known circuit diagrams / layout sheets date from close to this time.

A62/031, below, included by Jim Elyea in his "Schematics Portfolio", is one of two schemas for the T60 drawn up in October 1962. JMI presumably provided Burndept, the contractor charged with assembling the amplifier's chassis, with copies soon thereafter.

So far as one can tell, the first batch or batches of fully finished factory-made chassis - the "prototypes" mentioned - are likely to have been ready in or by December. The earliest T60s known to survive have components with November '62 date codes - notably the Woden interstage transformer (date code "LT").

The sheet as we have, based on one initially made in October 1962, was drawn up in January 1963.

JMI doubtless supplied Burndept with similar "real-world" layout sheets for the AC30 and other models - to be copied (and perhaps broken down into sections) for its work benches. More to come on Burndept's procurement and assembly procedures shortly.

Just to signal though - as has long been known - chassis were occasionally assembled in non-standard ways. That is certainly so in the case of a black panel T60 from late 1963: - components as other Burndept-made T60s, but no chassis number, and an eccentrically-arranged early-format (?) tagboard.

A black panel T60, no serial number. The latest visible elements are the potentiometers, which have the date code "KK" = November 1963 for their manufacture. Everything else is earlier: Woden interstage transformer dated November 1962, capacitors the 49th week of '62. There are signs that only two rectifier diodes were envisaged initially (earliest form of the T60 circuit) on the main tagboard, which was populated from factory in a non-standard way. On top of the chassis, rivets down the sides, a feature that has not come to light so far on other T60s.

The main power transistors are Mullard OC28s.

Early Pricelists

Neither the T60 nor the AC30 Super Transonic appear in any dated JMI pricelist from 1962 that has so far come to light. The latest list known from '62 is from 30th December.

The earliest listings for the T60 come (i) in the list attached to the "Choice of the Stars" fold-out catalogue; and (ii) in an advert placed in "Melody Maker" magazine, 2nd February, 1963.

Both of these lists give the same prices across the range. Where comparison can be made, these prices differ (upwards) from those of December 1962. Which is another way of saying the undated list attached to the "Choice of the Stars" catalogue is indeed from early 1963.

The strongest likelihood is that the T60 was not really ready for sale generally until '63. More on this in due course - something has already been said though on the updates page of the AC30 website, entry for 13th June.