Audio Note Tomei Kensei - Manual (Page 9)

Inspect a 211 valve and you will notice that there is a
small ‘pin’ protruding from one
side of the valve base; this locating pin ensures that the valve can only be correctly
inserted into the amplifier in one way.
Also examine the
two large apertures in the top plate of the amplifier, located
between the two small valves and the black rectangular transformer covers. These
are the insertion points for the 211 valves.
1)
Gently hold a 211 valve, and locate the small side mounted pin on the valve
base.
2) Line up this pin with the locating hole in the mounting aperture on the
amplifier’s top plate.
3) Gently insert the valve, and GENTLY twist in a clockwise direction, until the
valve ‘locks’ in position, and no more movement can take place.
Please make sure that steps (1), (2) and (3) are correct. Check again that both
valves are fully inserted correctly in to their respective valve sockets.
VALVE INSTALLATION continued…