Click to enlarge I possess a number of circuit cards like that in the top image (click on it to see a large version). Roger Holmes, a member of the UK Computer Conservation Society, has kindly given me a great deal of information about them. They are from the 1300 series mainframes manufactured from 1962 to the mid sixties by the British company International Computers and Tabulators (ICT). This historic company was formed from BTM, the British Tabulating Machine company which made IBM tabulators under license. It went on to merge with English Electric Computers, the makers of the KDF9 described elsewhere on this site, to form International Computers Limited (ICL), the commercial pinnacle of UK computer manufacture.

Roger is somewhat of an expert, as he owns and is restoring one of these computers which occupies about 500 square feet of a barn at his home. You can find more details of this astonishing project at his website. One of the key facts mentioned there is that Roger holds an annual 'Open Day' when the public can see this historic machine in operation. This is now part of the "Darling Buds Classic Car Show" held in July at Bethersden, near Ashford in the heart of Kent. More information is available on the Darling Buds site.

closeup of wirewrap The card shown is made of brown paxolin, 7 inches by 5 inches with 22 large wire-wrap pins at the front. It is fixed to a white plastic frame which also has 22 pins - the card pins are wrapped to the frame pins with heavy wire as shown in the image to the right.The frame pins have wires soldered to them, and the plastic itself has wiring guide slots. The card has two small handles, one green and one orange, Roger has told me that the colour coded tags identify the function of the board : in this case the orange-green is a drum track amplifier brick (all the cards are referred to as 'bricks' for some reason). The boards were mostly designed and built by GEC telephones in Coventry.

This card shown bears Mullard GET120 medium-power transistors, GEC GET103 transistors and Mullard OA10 diodes. I have a selection of different cards, some smaller, and all use exclusively semiconductors from these two British manufacturers. I even have some larger power supply boards with GEC GET573 or Mullard OC36T power transistors on them, and capacitors dated 1963 or 1964. The boards do not bear any logos or lettering, except for a small paper label stuck on the circuit side bearing a printed identifier: this card has "ED 40790/".

the ICT logo I have one example of this wire-wrap technology, albeit bearing unbranded ASZ21 transistors, which bears the logo ICT, as shown on the right. Roger tells me that this board does not come from the 1301, and may belong to its successor, the 1302.