Radiodoc is right 1626 is a triode. 1629 is the eye tube. It was used in test and military equipment. They are available from AES, Radio Daze and others. A 1629 has an octal base while 6E5/6U5 have 6 pin bases so are not interchangeable.
:You sure that eye tube is not a 1629.
::I have restored a Heathkit C3 capacitor checker. However the green glow of shadow tuning tube can only be seen in total darkness. Disconnecting the 47k resistor increased the voltage on pin 4. That helped but only very little. All voltages appear normal.
::The tube is a 1626, as specified in the manual. I cannot find any ref to this tube. Can a 6E5 or 6U5 be directly substituted? Was 1626 Heath's own number to promote tube sales or is the tube really unique?