The B&K 707 operators manual states the minimum/good range for a 12AX7 tube is a reading of 22. A reading of 22 is equivalent to 60% Gm. New 12AX7 normally tests 32 and above. See photos for test results.

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The B&K 707 operators manual states the minimum/good range for a 12AX7 tube is a reading of 22. A reading of 22 is equivalent to 60% Gm. New 12AX7 normally tests 32 and above. See photos for test results.