Matched pair (2) boxed GEC KT66 with matching code "RE Z".
Tested with Amplitrex AT1000:
Tube #01 : iP=78mA(92%), GM=6.35mA/V(101%)
Tube #02 : iP=79mA(93%), GM=6.20mA/V(99%)
Spec : iP=85mA, GM=6.3mA/V