Nel 1925, Mullard ha venduto metà delle azioni della società Mullard a Philips , con il resto della società incorporata da Philips nel 1927. Dalla fine degli anni 60, sino alla fine degli anni 70, in Mullard fu adottata una politica basata sul contenimento dei costi che, gradatamente, portò il prodotto a perdere di qualità sino al 1981 anno in cui Mullard cessò la produzione.
Mullard Blackburn ECC83 codes
mC Series usually have 17mm plates.
mC1: circa late 1955 until early 1958; 17mm plates, square getter with double crossbars on 2 support posts.
(*mC1-etched tubes were also made by Valvo Hamburg and Siemens-Halske Munich; different physically and sonically)
mC2: Valvo Hamburg
mC3, mC4: never seen one
mC5: Philips Heerlen
mC6: Philips Heerlen
f91: late 1957 until early 1959; 17mm plates, halo getter on 2 support posts.
f92: late 1958 until late 1959; 17mm plates, halo getter on single support post, anti-microphonic pattern cut out of top mica spacer and balanced on grid posts.
I6 series usually have 14mm plates
I60: Valvo Hamburg
I61: mid 1959 until mid-late 1964 or so; 14mm plates, halo getter on single support, anti-microphonic pattern. Early (1959, some 1960) have silver-colored grid posts; later have copper. After late 1960, acid-etching has fourth digit in second line indicating week of month. Acid-etching can be lighter in color, and may be upside-down.
I61 also Philips Heerlen, different
I62: Siemens Munich
I63: late 1964 or so into the 70's; 14mm plates, halo getter on single support, anti-microphony pattern, silver-colored grid posts. Chevron (or Optimus Prime grin emoticon ) logo shows up at the end of the 60's, replacing the old Shield logo.
I63 also Philips Heerlen, different
I64: Siemens Munich
I65: Siemens Munich and Philips Heerlen
If there is a "B" in the date code and the first number is between 0 and 5, you're looking at the real thing. The "B" means Blackburn, and the digit is the last number in the year (ie, 1960 to 1965). If there are only three characters in the date code, it is likely to be from the late 1950's. Most of the 60's versions have four characters.
Mullards with OEM labelling include:
Bausch & Lomb
Bell & Howell
Voice of music