Recommend new EL84 tubes

Sure, if the tubes are overdriven they won't last. Perhaps Kevin doesn't sell the Gold Lions. 🙄   In his video he's talking about putting an EL34 into an amp that is biased to run KT88s and so driving the plates beyond their rated max. dissipation.

I am considering the Gold Lion EL 84 because the Manley has provision to set the bias individually via trim pots. Have you heard these tubes? I am, of course interested in how they stack up to the originals

Jim McShane says basically the same thing but it doesn't apply to most consumer audio components including Manley. Jim references the Vox AC-30 and AC-30 clones; guitar amps that run the output tubes beyond dissipation specs. I know this to be true as I own an early 1966 Vox AC-30; bad ventilation to make matters worse. Guitar players call this design the "easy bake oven".

I have tracked down some Brimar/Marconi black plate 1950s 12AT7 but have not yet decided on el84s

Brent Jesse of audiotubes.com suggested Mazda of France EL84 tubes as replacements for the JJEL84 in our Luxman NQ150 integrated amp. Was not originally happy with the Mazda tubes, but after 60+ hours they came into their own. Great sound.

+1 Brent Jesse. Great for NOS tubes.