Thanks for the link... lots of good info there. I went ahead and ordered some 8.2 devices, will give them a try to see what they do to the RMS voltage at the 7JP4 heater pins during turn on surge and normal operating conditions.
Still scratching my head over the specs that you posted, will try to determine the slope of the voltage vs current curve around the 8.2 voltage point. Possibly it could have considerable slope.
jr