Date codes of Hunts capacitors in Vox AC100s
The Hunts factory, in contrast to Dubilier and TCC (both in North Acton), was in south London - Earlsfield, not too far from Wimbledon. The works formerly belonged to (and were originally built for) the Columbia Gramophone Company.
Picture from the Britainfromabove website. Note in the foreground a vast array of allotments.
Hunts was taken over by Erie in the late 1960s, probably 1969.
Most of the grey panel AC80/100s have blue Hunts 25uf caps for the preamp valve cathode bypass (C3 and C4). The change to the light gold 25uf TCC "Micropack" seems to have taken place between serial numbers 392 and 420.
Above, a detail of AC100 serial number 392 - Hunts cathode bypass caps at left.
The spent capacitors removed from the amp - date code is "IYT" = 30th week of 1964.
The Hunts date code system
The key to the Hunts code was worked out some years ago on a British valve radio forum with the help of a former Hunts employee.
The system is based on the word "WHITSUNDAY", chosen because it has ten letters, none of which are duplicate. W = 1, H = 2, I = 3, T = 4 and so on, through to Y = 0.
To decipher "IYT": the first two letters give the week of the year, in this case 30, ie. the 3oth week. The third letter gives the last digit of the year of manufacture, in this case "T" = 1964.
There are instances, however, when the code appears to have been given in reverse order, the first letter being the year, and the second and third the week.
Above, a Hunts cap. with the code "D YW". This is also to be deciphered year first, then week of year: "8 01" = the first week of 1968.
Some general points
Legibility naturally depends on the way in which the cap was soldered in. On the whole, bias and cathode bypass caps provide more instances of date codes than the large preamp filter caps, which are held in with clamps that obscure substantial portions of the Hunts legends. But one can sometimes see relevant date code letters peeping out.
Clearly one does not know how long new capacitors sat on stockroom shelves. Any estimation is just a guess or surmise. But in numbers of cases date codes are exceptionally useful for locking down the terminus post quem - the date after which an amp must have been made.
The proviso of course in all cases is that caps are original to the amp.
An overview of codes in AC100s
Jan. 2019 - further details to follow
Serial number 1367. The Hunts preamp filter caps have the codes: "IUS" and "UYT" = 36th week of 1965 and 4th week of 1966.
Assembled by Triumph. Underchassis signed in pencil, perhaps by "Graham". The blue Hunts 16uf capacitor has the code "HUS" = 26th week of 1965.
The date code of the blue Hunts 16uf capacitor in the preamps of a number of AC100s with serial numbers in the 1900s - starting with no. 1905 - is "UYT" = 4th week of 1966. Notes have been added where relevant on this page. Given no. 1367 above, stocks evidently lasted some time.