Dave Plowman wrote:

So I removed the transformer, and series the windings. On UK mains,
under 500mA load, the heater volts are 7 volts rather than 6.3 which
makes sense if the windings are 110 volt. Will this matter?

Never been in that situation, but...

http://www.burdaleclose.freeserve.co.uk/new_page_33.htm

....says...
---------------------
Filament and heater voltages should generally be maintained within ± 7 per
cent of the rated values. The heater current of valves connected in series
should be maintained within ± 5 per cent of the rated values.
Thoriated-tungsten* and oxide-coated filaments should be maintained within
closer tolerances than the above figures: 5 Per cent voltage fluctuations
are permissible, but permanent deviation from rated value will reduce valve
life. Directly heated and indirectly heated valves having similar filament
current ratings should not be connected in series.

---------------------


And a couple of comments from...

http://www.diyaudio.com/forums/showthread/t-13340.html

---------------------
Mullard quote 5% tolerance on heater voltages, but mains voltage varies, so
AC heaters need to be set as closely as possible (and ideally measured with
a true RMS meter). Regulated DC supplies can be set to precisely the correct
voltage, so it seems foolish not to do so...
---------------------
I recall reading a long time ago that every %10 high your filaments are,
your tube life get's cut in half.
---------------------

If you're getting bang on 7V, then that's a shade over 11%, which might be a
bit high if the above are anything to go by. I suspect that the same will
happen to the HT lines, and that could result in the biasing of the valves
being slightly out - could be an issue if the unit is supposed to do precise
measurements.

You could risk it, but maybe a 240-110 step down transformer is the safest
option.


--
Wally
www.art-gallery.myby.co.uk
Latest work: The Langlois Bridge (after Van Gogh)