Hi,

Hope some of you can help me with the following puzzle.

Measuring six brand new 12AX7 on my B&K (Bruel and Kjaer) 606 Dyna-Jet tube tester, this machine tells me to replace them all. (the meter indicates 10-20, where at least 65 is “good”). Grid emission is okay, according to the 606.
Three other 12AX7, about 4 years old and also never been used, measure the same, 10-20

Of course all settings of the tester are correct and 12AX7 of different brands measure without any problem. Just like the tube tester measures all other types of tubes correctly. For instance,no problems on measuring EL34 from Electro Harmonix.

Is there something special on 12AX7 I must take care of?
I would be grateful of any help or suggestions!

Beur