I switched to 6L6s out of desperation to have a working amp. Yes, EL34s have great tone, but they're pretty fragile in comparison. There are some 6L6s that are really sweet though.
About 3 months ago I stuck a quad of Groove Tube 6L6GE cleartops in my Lynch Box. I adjusted the bias to about 35 mV. It took them about a month to burn in. They are killer.
But be careful with that screwdriver. Those trim pots are pretty sensitive. A little tiny turn can make a difference. So don't be agressive with the screwdriver.