Which amp? You didn't post it.

6L6 tubes usually used in configurations that have that nice big beefy Fender sound.

EL84 tubes are often employed in a manner similar to classic Vox amps.

Both can get good clean sounds, but quite different in tone and timber and depth.

I've known folks to use the Yellow Jackets.  They work, but you might also consider getting an amp with EL84 configuration instead.

But if you really want to try the Yellow Jackets, I say give it a try.  Keep your options open.  Cheaper to buy the Yellow Jackets than a used amp.

Make sure you have enough room, Yellow Jacket is basically like a socket adapter.  It goes into the footprint of the 6L6 socket, and then the EL84 goes into it.  So it might stick up to far in some configurations.  I think they make shorter ones now that are just a bit more expensive.

Also, make sure you screw down the ground wire as instructed.  Only problems I've ever heard of had to do with people skipping that important step.

It will take your typical Class A/B config and make it a cathode-biased Class A using EL-84 tubes.

Bear in mind that they will be considerably brighter than your 6L6 tubes.

I don't know how cranking up your amp to 10 with this make-shift conversion going in will affect the hardware and electrical components in the long run, but you will be able to crank up the power because it will be about 1/5th of the power when using the Yellow Jackets.

Good luck, and tell us how it goes.

Peace

phil