A Valvo E88CC. The codes are " D 6 L " and it was made at

 VALVO  tube plant in HAMBURG in 1956. Tested perfect and

 strong at 11 / 11 where 15.0mA is the nominal value for an

 unused tube. It is also tested good for gas,leakage and shorts. D-Getter and pinched waist.

This tube is rare as hens teeth! Especially in this stunning condition. A true colllectors tube.