Reporting question for Vacuum Tube - 12AY7, Triode, Dual

Vacuum Tube - 12AY7, Triode, Dual

What is the diameter of the glass envelope on this nos 12AY7 ? I need this tube for an AKG c-28 microphone. I have found that most new 12AY7's are too large in diameter at 23cm to fit inside the mic body. The original GE tube is 21cm in diameter. Thank you.

At 21cm you would be looking at a tube with a diameter just over an 8 1/4" and that is too large. These 12AY7's are 13/16" (20mm) in diameter.