The ARRL handbook, et al, merely mirror the information that has come
out of the tube industry's long-running standards for tube bases. Your
observation of the numbering system is pretty much correct. The final
"authority" was probably the old RETMA manufacturing consortium that set
the then-standards for tubes and many other electronic components.

wrote:

In my circle of tube usage, we always speak of tube bases like "6BA6
and 6AU6 both have the 7BK basing". Then I look in my oldish ARRL
handbooks, find the chart of tube bases and see the 7BK pinout.

Many of the tube databases on the net use the same terminology for
bases.

Obviously for the number-letter or number-letter-letter bases the
number is how many terminations. And the letters seem to have been
assigned sequentially (or maybe not?)

And there are some oddball bases (power tubes etc.) that don't follow
the number-letter pattern but instead are simply numbers.

Is the ARRL handbook the "final authority" on tube basing, or (more
likely) is this simply an excerpt from a more authoritative list
somewhere else?

Tim.