They are NOS and absolute pristine in both performance and apperance.Genuine Mullards with identical codes: B9K1 and B9K3. Made at Mullards tubeplant in Blackburn in 1969.
Matched Factory code:R9D(1959 Apr. made). NOS Match 1 pair Mullard ECC81 TUBES. NOS 1 pair Mullard TUBES ECC81 foramplifier. Type : ECC81. Smooth plate/SQ getter. Rectifier 5U4/5Z3/GZ32/6X4. Vacuum very specialized and complex issues involved .
Beautiful pair of Mullard 12AX7 long plate square getter mC1 tubes, with identical shield logos. Perfectly matched and balanced for Gm on the Amplitrex AT1000. 1957 Blackburn, UK, date codes. Date codes mC1 B7B & mC1 B7F.