OT - A question for the valve experts.
 

"Nick Gorham" wrote in message
...
Dave Plowman wrote:
I collect old test gear as a hobby, and like to have it working too. I
recently bought a 110v valve sig gen in very nice condition and it works
fine off a 110 supply.

Looking inside - as you do - I noticed that the transformer primary was
two windings in parallel. This, of course, is common these days -
parallel
operation for 115 volts and series for 230.

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?


Just a bit more that +10%, I suspect it could shorten the life of the
valves a bit. How many valves and what are they, 500ma is less that two
ECC83's (for example) would take, it may be that under actual use the
voltage would be lower that that. HT will I guess be a bit high as well,
but 10% shouldnt make that much of a difference.

Other option (as I am sure you know) would be to measure the primary
current and add a small dropper resistor.

Having wrote all that, I am tempted to say, no it probably won't matter.



Hmmm, I wouldn't worry about +10% (max) heater voltage on an amp running
summat cheap/plentiful/tough like a bunch of 5881s (or similar) but I
personally wouldn't knock a matched pair of WE300Bs about with that much
extra voltage. Test Gear though? - No, I'd sooner see that figure yanked
back a lot nearer to the line, like you say.....

OT - A question for the valve experts.
 

Form@C wrote:


You should get away with it as this sort of equipment isn't usually left
on for days on end - at this time of its life, anyway! If it worries you,
connect the AC terminals of a small bridge rectifier in series with the
heater winding. That should drop enough volts to keep things happy.
(ignore the + & - terminals).


I think you mean "connect together" rather than "ignore".

--
Roger.

OT - A question for the valve experts.
 

Form@C wrote:


You should get away with it as this sort of equipment isn't usually left
on for days on end - at this time of its life, anyway! If it worries you,
connect the AC terminals of a small bridge rectifier in series with the
heater winding. That should drop enough volts to keep things happy.
(ignore the + & - terminals).


I think you mean "connect together" rather than "ignore".

--
Roger.

OT - A question for the valve experts.
 

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
...
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)

OT - A question for the valve experts.
 

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
...
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)

OT - A question for the valve experts.
 

On Sat, 13 Dec 2003 16:56:02 +0000, Old Fart at Play wrote:

Form@C wrote:


You should get away with it as this sort of equipment isn't usually left
on for days on end - at this time of its life, anyway! If it worries you,
connect the AC terminals of a small bridge rectifier in series with the
heater winding. That should drop enough volts to keep things happy.
(ignore the + & - terminals).


I think you mean "connect together" rather than "ignore".

ulp.... yeah! Sorry 'bout that! :-)

--
Mick
http://www.nascom.info for Nascom & Gemini information
Also at http://www.mixtel.co.uk where the collection started.
Currently deserting M$ for linux... :-)

OT - A question for the valve experts.
 

On Sat, 13 Dec 2003 16:56:02 +0000, Old Fart at Play wrote:

Form@C wrote:


You should get away with it as this sort of equipment isn't usually left
on for days on end - at this time of its life, anyway! If it worries you,
connect the AC terminals of a small bridge rectifier in series with the
heater winding. That should drop enough volts to keep things happy.
(ignore the + & - terminals).


I think you mean "connect together" rather than "ignore".

ulp.... yeah! Sorry 'bout that! :-)

--
Mick
http://www.nascom.info for Nascom & Gemini information
Also at http://www.mixtel.co.uk where the collection started.
Currently deserting M$ for linux... :-)

OT - A question for the valve experts.
 

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

OT - A question for the valve experts.
 

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

OT - A question for the valve experts.
 

"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