Mullard/Amperex 12AU7A made in India Delta 0? very strong trio,  no other information, tested with Hickok 800a where new is 2200 micromho's: Results, Tube #1=1850/2100 Tube #2= 2250/2050 tube#3= 2050/2000. Auditioned with heath-kit w5m Genelex KT66 mono-block, with custom made folded horn, Stromberg Carlson 15" 

Tube's sounded same compared with known Mullard .

Silkscreen is consistent for the age and construction