I believe it's time to re-tube my Mesa Express 5:25

Over the past few months, the first time I switch on the amp, let it warm up, and start playing, about 2-5 minutes into playing it'll pop, volume will drop down to practically nothing, and then it'll pop again, and start screeching for about 5 seconds. Stop. Sound ok for about 20 seconds, then do it again.
If I turn the amp off, then back on, it won't do it again.

Over the last two-three weeks, I've noticed I've been losing volume after a short period of playing.

It has 2 EL-84's for power tubes, and 5 12AX7's in the pre-amp.

What would be some good tubes to replace these?
PRS SE Custom 24
Jackson DKA7
Gibson Explorer
MESA/Boogie Express 5:25

Dunlop Cry Baby Classic
VOX Joe Satriani Ice 9 OD Pedal
VOX Joe Satriani Time Machine Delay Pedal
Ernie Ball Strings
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