I have been playing around with power valves on my main full on leak stereo 20. I am using Mullard EL84s the ones with the hole in the plate, long considered the best EL84, A statement i have to agree with, and the best I have heard to date. They are even better than the genuine Amperex EL84s with the half triangle but only a little. I decided to try a brand of tube that i must say is overrated, the Telefunken, So in went 4 expensive new Telefunken EL84s, I have about 20 of them, but never used them, well i must say these are very good indeed in many ways better than the Mullards, Impressive tubes they sound sweet pretty uncluttered and have a ease about them, always taking complex classical music in there stride, i may leave them in this amp, time will tell, They are definitely needed in the tube arsenal for this amp, but i am only talking about there EL84 Variety, other types of Telefunkens, will have to prove themselves at another time, and in another amplifier.