with a 2.24v grid bias you can feed them almost 4.5 volts before you get grid current on the input valve. Perhaps 4.3 volts peak, or +/- 4.3 v would give a better idea of maximum output at the anodes. High gm valves probably get a bit of early grid current. Certainly the lower gm 6H30 gets grid current before its cousin the 6H6.... regards, Douglas