12AX7 / ECC83 Mullard Tube. Made In Great Britain. 

• Manufactured in Blackburn Factory 1965 September First Week

 TV-7D/U: Tested Good.

• Twin-Triode Vacuum Tube 

• Triode:1 Tested Good: 42/ 32 Baseline.

• Triode: 2 Tested NOS: 52/ 32 Baseline.

• Ribbed Short Plate
• Cross Top

• Top O Getter.  
• Date Code: B5I1

Testing & Condition

• Minimum reading: 65% (per original 32 baseline; military standard).
• Tubes test NOS and meet or exceed published GM data.
• All tubes tested for gas, shorts, transconductance, and emissions.
• TV-7 tested (calibrated, military-standard tester). 

About NOS & Testing

• NOS tubes fall within the GM range published in the RCA Receiving Tube Manual; variation above/below average is normal.
• No universal test result defines NOS. Typically, NOS tubes measure between average and maximum micromhos.
• Different testers (even identical models) may produce different readings.
• 100% meter readings are not required?passing = meeting spec range or minimum (TV-7: ~65%).
• 12AX7 Minimum Range: 32.
• 12AX7 Nos Range 45 +.