[Amps] SB221: Can you saftely mix and run an Eimac 3-500Z with and RF Parts 3-500ZG-RF ?

[Jeff King]

A question from a new comer. While rebuilding the SB221, I turned it on at
final test and one tube did not light well, then after about 15 seconds long
15 mm long sparks in side near the base, then does not light at all, and it
is slightly whiter inside. Dam!

I need another Eimac 3-500Z. (Not easy to find, Only 3-500ZG is available
new.)
One reads occasionally that it is not so important to have matched pairs of
tubes. How much can you safely miss match tubes? Does this extend so far
that one could run an different brand tube, Ie an RF parts 3-500ZG-RF or a
Taylor 3-500ZG with and Eimac 3-500Z?

You will probably laugh at this. Does anyone have knowledge of safely
running such a pair of different tubes?

I look forward to your advice.

Yours sincerely
Jeff ZL:4AI