Ok thanks everyone for their input ... I was under the impression that
the MLA-2500 was a well built amp, and easily modifiable to use less
expensive available tubes.
I'll do some further research.

I would not say it is easy , but I seem to remember that in a 73 Magazine
(maybe QST) there was an artical to modify it for one of the single Russian
power tubes. Doubt that I would go to that much trouble as there are many
of the Heathkit and other amps around that use a pair of the much more
rugged
4-400 and 3-500 type tubes.