12AT7WA, Heintz & Kaufman, Gammatron, ECC81, USA 1973 production,

12AT7WA, Heintz & Kaufman, Gammatron,  ECC81, USA 1973 production,

On offer today is a lovely Heintz & Kaufman 12AT7WA, a premium quality ECC81 carrying the date code for 1973.

Carrying slightly smudged yellow 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 = 11 mA; gm = 5.4 mA/V

Section 2: Ia = 11 mA; gm = 5.1 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.