Looking back EL84 failed tubes was the issue on the last 5 blues JR amps I looked at. I only have two amps that use EL84's this is the only EL84 I will use in my amps
it can take 450v and last 5,000 hours.
https://www.tubedepot.com/products/sovtek-el84m-power-vacuum-tube
I got a box of 50 direct from Russia they are not made now so get them while you can.