I picked up a box of tubes locally with many types of NIB/NOS Amperex BB. and in the mix there were a few of the legendary EL34's. I am not going to tell you how fantastic these tubes are, I will say that I have four on my Quick Silver mono blocks and they are singing like never before. Tested on a calibrated B&K 747B mutual conductance tube tester. The tubes tested at 105, 107, 107, & 108, passed shorts and grid leakage test. Life test held well above 110 on all four. New is 100% I was going to rate them 9/10 but the boxes are a bit dirty. Etched code is XF4-Loi. Ok, you win, times are tough so first $750.00. takes them.