(!!) (Best Single 1966) ECC83=12AX7 Siemens Halske Germany NOS 1966 (162 Series) (Gm=1500/1600 and 1.0/1.1ma)
(!!!!) (Best Single 1975) 12AX7=ECC83 Mullard England ribbed plates NOS 1975 (163 Series) (1.3/1.4ma and Gm=1800/1800)
(!!!!) (Best Value 1965) 12AX7 Philips Miniwatt Holland like new 1965 (Gm=1900/1700 and 1.5/1.2ma)
(!) (MULLARD CLONE) 12AX7=ECC83 Matsushita Japan used/good 1960's (Gm=1450/1250 and 1.3/1.1ma) (similar to Mullard)
(!!!!!) (Recommended Single) ECC83=12AX7 Telefunken Germany smooth plates NOS 1972 (1.3/1.3ma and Gm=1700/1700) 1% section balance
(!!) 12AX7A/7025 Sylvania branded RCA NOS 1970's (Gm=2100/2000)
