Despite having 6-800 hours on them, ten of the twelve tested between 100 and 110 on a tube tester, and the other two came out between 85 and 100. This was using the sensitivity set at 53, per that tester's standard for the tube type.this number refers to the "mutual conductance" (a.k.a. transconductance) that the tube delivers in the tester's circuit, which is a representation of the change of plate current divided by the change in grid voltage. With output tubes, this translates to "power gain" (power output vs. AC grid voltage), not maximum power output before clipping.
Maximum power output before clipping in a tube amp is a function of the plate voltage, the tubes' plate resistance (Rp), the load impedance (the speaker load impedance multiplied by the square of the output transformer's turns ratio), and the output transformer's insertion loss. All of these factors except for Rp are part of the amp, not the tubes . . . and this tube parameter tends to be less variable than transconductance.
Also note that "Pa max 25 watts" does NOT refer to the maximum power of an amplifier using this as an output tube, rather it refers to the maximum amount of power the tube's plate (a.k.a. anode) is able to continuously dissipate. (Pa = "anode power"). Plate dissipation is a function the quiescent (idle) conditions, the loading, and the duty cycle. I've personally measured almost 220 watts output from a quad of "25 watt" EL34s, running push-pull pentode with about 730 volts on the plates.
