On offer today we have a Brimar white print 12AX7 made at the Brimsdown plant and carrying a date code for December 1960.
For Va = 250 V Vg = -2.0V against a nominal specification of anode current Ia = 1.2 mA and mutual conductance gm = 1.6 mA/V, the following results were obtained:-
A1 Ia = 1.4 mA gm = 2.1 mA/V
A2 Ia = 1.4 mA gm = 2.0 mA/V
As you can appreciate this represents good matching of each triode section within the envelope and a device showing superb emission.
