Vox AC100 mark 2 capacitor date codes
Three suppliers - Daly, TCC (the Telegraph Condenser Company) and Radiospares - used the standard British component date-coding system - two letters, the first for the year, the second for the month.
A fourth - Hunts - had its own (highly idiosyncratic) system - see further below.
The dates printed on original components necessarily give one a useful terminus post quem (date after which) for the making of the amp. Potentiometer date codes are outlined on this page.
Daly, TCC and Radiospares
YEAR: W = 1965, X = 1966, Y = 1967.
MONTH: A-M (omitting "I") = January to December.
"WH" = August 1965, "XE" = May 1966, "YF" = June 1967, and so on.
An early AC100 mark 2 (no serial number). On the left-hand gold TCC cathode bypass cap, "WD" = April 1965.
Date codes on green TCC micromite preamp filter capacitors are often difficult to see, hard against the chassis.
Daly filter capacitors from serial number 1584, date code "XB" = February 1966.
Radiospares filter capacitors from a late AC100, date code "YF" = June 1967.
Blue Hunt capacitors have an altogether different system. The key is the word "WHITSUNDAY", chosen because it has ten letters, none of which repeat. W = 1, H = 2, I = 3, T = 4 and so on, through to Y = 0.
To decipher "YIU": 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 "6" = 1966.
Serial number 1579 - Hunts capacitor, date code "YIU" = 3rd week of 1966.
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. (not from an AC100) with the code "D YW". This is to be deciphered year first, then week of year: "8 01" = the first week of 1968. It can hardly be the 80th week of 1971.