This CV4004 is an example of the Brimar special quality version of the ECC83 possessing the quasi-boxstructure anode which imparts supreme rigidity with a consequent deep, dark and extended sound in audio applications.
Manufactured to an exacting standard for the British military by Brimar at their UK Rochester plant as evinced by the KB/AD factory code. Their military useage was in many different applications but all of which required ruggedised construction, supreme longevity - up to 10,000 hours service life - it seems almost churlish to fit these exquisite devices to audio equipment destined for the living or listening room!!!
This example is ex-equipment an carries the UK military date code XA which equates to January 1967. It tests as GOOD using my AVO Valve Characteristic Meter VCM163 with the following results: At Va = 250V Vg = -2.0V
Section 1: Ia = 1.0mA; gm = 1.6mA/V
Section 2: Ia = 1.2mA; gm = 1.9mA/V
The specification for a new/100% emission valve is:
Ia = 1.2mA; gm = 1.6mA/V
As you can see, this result show a strong valve with good matching of each triode section within the envelope.