On offer today is a lovely Marconiphone premium quality ECC81 . Carrying good white print, it tests as excellent using my AVO Valve Characteristic Meter VCM163 with the following results: At Va = 250V Vg = -2.0V
Section 1: Ia = 10 mA; gm = 5 mA/V
Section 2: Ia = 10 mA; gm = 5 mA/V
The specification for a new/100% emission valve is:
Ia = 10 mA; gm = 5.5 mA/V
As you can see, this result show a strong valve with excellent matching of each triode section within the envelope.