The T307 is a Japanese special triode. The anode is taken to the top cap. In our specimen the top cap itself is missing but the wire from the anode is visible.
The information supplied by Hiroshi Sakai is that this valve is a modified form of 6L6.
The envelope itself has Japanese text.
The wide glass tube envelope is 37 mm in diameter and, excluding the B4 base pins, is 98 mm tall.
References: Observation & Hiroshi Sakai.
Updated January 05, 2013. shape:wide.glass.tube construction:pinch type:triode base:b4 pins:4 pin: