I ask this because of nonstandard name (not like industrial tubes), thanx for information
The wonderful things about standards, is there are so many to choose from!!!!
The 2E26 number comes from the RMA 1942-1944 system. It is very standardized. First number is the heater power; 2 means less than 10 watts. The letter is type of device; E is a pentode. And the last digits are a serial number, starting with 21.
Incidentally... there are some other devices widely available to this day from the same numbering system. e.g. 1N34 means this: 1 means no heater power. N means crystal rectifier. 34 is a serial number. Thus... the number for the 1N34 germanium diode comes from the exact same system as the 2E26 tube.
See Sibley's _Tube Lore_, or http://en.wikipedia.org/wiki/RMA_tube_designation