Bought a matched pair of French EL3Ns from eBay - NOS NIB but no amp to listen to them. Also bought ceramic bases and adapters. The adapters will allow you to insert the tubes into most pentode amps but ensure voltages and currents are correct. I was lucky both were close enough.
From what I have read you should run the tubes in triode strap but for me who loves UL I left them as the amp had been wired for 6L6. In UL you get a little more power and I feel extra drive. Whatever, they sound extremely good and with one of my wine box 6L6 amps the tubes hissed but in the other (same schematic and parts values) dead quiet. You can get these tubes quite cheap but I paid a premium and again "whatever" a very pleasing audio result.