EL34s are not direct replacements for 6L6s. You can get a 6L6 amp modded to accept EL34s. After the mod, you can switch between EL34s and 6L6s with just a bias adjustment. Some amps have the swapping capability already built in, like the Peavey Triple XXX amps.
A less radical approach would be to swap out the 6L6s for 5881s, no mods needed.
6L6 sounds better than 5881s base on my experience.
I really do not have a lot of experience with 5881s, just EL34s and 6L6s. All I know is that the 5881s have lower headroom and breaks up sooner than the 6L6s.
OT ubersam,is that a dual recto road king on your avatar?Someone is selling me a 3 channel triple rectifier for 1000k 2 yrs old.Have you tried it?I have tried countless rectos but not the roadking and the triple rect.Should i get it?Yes i love hi gain amps.
Ya, my avatar is a pic of the logo on my road king. So someone is selling you a 3-ch triple rec for 1000K, wouldn't that be 1m? I assume that you meant $1KUSD. That seems to be on the high side of used prices, 800 to 900 would be better IMO. For 1K, I would expect an immaculately clean and blemish-free item. Anyway, AFAIK, the Road King is essentially a 4 channel Dual Rectifier with a boat load of options per channel. The additional clean channel on the RK is taken from the Loan Star. With the exception of the Loan Star cleans, you should be able to dial in the same sounds from both the RK and the Triple Rec.