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)

I agree with Wally, use a 240-110 stepdown transformer then at least you'll
know the heater and HT lines are correct. No point in risking altered bias,
high heater voltage possible elevated HT & shortened tube life - not to
mention your own peace-of-mind :-)

Mike

"Wally" wrote in message
news
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)

In article ,
Mike Gilmour wrote:
I agree with Wally, use a 240-110 stepdown transformer then at least
you'll know the heater and HT lines are correct. No point in risking
altered bias, high heater voltage possible elevated HT & shortened tube
life - not to mention your own peace-of-mind :-)

I've already got a 110 v transformer for power tools, but it's a big
b***ard. And I don't want the faffing around of using one anyway. Also, if
I had to buy a smaller, more suitable one, I might as well just replace
the sig gen transformer with a 240 volt one - like all equipment of this
age there's plenty of room inside.

--
*Real men don't waste their hormones growing hair

Dave Plowman London SW 12
RIP Acorn

"Dave Plowman" wrote in message
...
In article ,
Mike Gilmour wrote:
I agree with Wally, use a 240-110 stepdown transformer then at least
you'll know the heater and HT lines are correct. No point in risking
altered bias, high heater voltage possible elevated HT & shortened tube
life - not to mention your own peace-of-mind :-)

I've already got a 110 v transformer for power tools, but it's a big
b***ard. And I don't want the faffing around of using one anyway. Also, if
I had to buy a smaller, more suitable one, I might as well just replace
the sig gen transformer with a 240 volt one - like all equipment of this
age there's plenty of room inside.

--
*Real men don't waste their hormones growing hair

Dave Plowman London SW 12
RIP Acorn

Better still. As its in decent condition then its sure worth the minimal
effort of replacing a transformer. Back in the 80's I knew a retired RRE
boffin living in Malvern whose hobby was just collecting test gear and
bringing it back exactly to spec. When he died the house was literally full,
gear stacked high with 'alleyways' in between. It was all actioned off.

Mike

"Dave Plowman" wrote in message
...
In article ,
Mike Gilmour wrote:
I agree with Wally, use a 240-110 stepdown transformer then at least
you'll know the heater and HT lines are correct. No point in risking
altered bias, high heater voltage possible elevated HT & shortened tube
life - not to mention your own peace-of-mind :-)

I've already got a 110 v transformer for power tools, but it's a big
b***ard. And I don't want the faffing around of using one anyway. Also, if
I had to buy a smaller, more suitable one, I might as well just replace
the sig gen transformer with a 240 volt one - like all equipment of this
age there's plenty of room inside.

--
*Real men don't waste their hormones growing hair

Dave Plowman London SW 12
RIP Acorn

Better still. As its in decent condition then its sure worth the minimal
effort of replacing a transformer. Back in the 80's I knew a retired RRE
boffin living in Malvern whose hobby was just collecting test gear and
bringing it back exactly to spec. When he died the house was literally full,
gear stacked high with 'alleyways' in between. It was all actioned off.

Mike

In article ,
Mike Gilmour wrote:
I agree with Wally, use a 240-110 stepdown transformer then at least
you'll know the heater and HT lines are correct. No point in risking
altered bias, high heater voltage possible elevated HT & shortened tube
life - not to mention your own peace-of-mind :-)

I've already got a 110 v transformer for power tools, but it's a big
b***ard. And I don't want the faffing around of using one anyway. Also, if
I had to buy a smaller, more suitable one, I might as well just replace
the sig gen transformer with a 240 volt one - like all equipment of this
age there's plenty of room inside.

--
*Real men don't waste their hormones growing hair

Dave Plowman London SW 12
RIP Acorn

I agree with Wally, use a 240-110 stepdown transformer then at least you'll
know the heater and HT lines are correct. No point in risking altered bias,
high heater voltage possible elevated HT & shortened tube life - not to
mention your own peace-of-mind :-)

Mike

"Wally" wrote in message
news
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)