Date codes of Hunts capacitors in Vox AC50s
Blue Hunts electrolytic capacitors were used extensively by Triumph Electronics, the company that first assembled AC50s under contract for Vox, throughout 1964 and 1965.
A selection of values were bought in for the circuit, which required: four 25uf 25v for preamp valve cathode bypass; two 8uf 150v for the bias circuit; one 32uf 450v for preamp filtering along with two 16uf 450v; and two 32uf 500v as main power amp filters.
Above, a couple of details of AC50 serial number 1411, large box. In the first picture, four Hunts cathode bypass capacitors, one with the code "WST"; also, the main preamp filter caps. In the second picture, the two caps in the bias circuit, one with the date code "HWT".
The Hunts date code system
Above, a Hunts filter cap from AC50 serial number 1034B. Its twin is still in place in the amp. The date code is the three letters: "YIW".
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 "YIW": the first two letters give the week of the year, in this case 03, ie. the 3rd week. The third letter gives the last digit of the year of manufacture, in this case "1" = 1961.
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. "ITD", found in another two input amp made a little later in 1964, translates as 348, which must mean 1963, 48th 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.
Above, an aerial view of the Hunts factory in south London - Earlsfield, not too far from Wimbledon. The works formerly belonged to (and were originally built for) the Columbia Gramophone Company.
Hunts was taken over by Erie in the late 1960s, probably 1969.