The extra voltage on the ECF80s is 'normal' but not necessarily desired.
You must test it with
all the valves in though, to get a true reading.
That way the transformer is loaded correctly and you are not measuring just the 'peak' DC voltage. It won't hurt the ECF80s for a few minutes.
Once you know the actual working DC voltage you can work out a resistor to get it between 6 and 6.6 volts. (Assume 2 x ECF80 consume 0.9A) Most people have ended up with a 1 ohm 3 or 5 watt job.
There is a 'Mod' too if you look here:
http://www.world-designs.co.uk/forum...ead.php?t=7644