OT - A question for the valve experts.

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?

--
*All men are idiots, and I married their King.

Dave Plowman London SW 12
RIP Acorn

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.

--
Nick

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.

--
Nick

Not a valve expert, but i would think:

a) each heater would draw more current.
b) valve reliability would go down.
c) valve transfer characteristics would change slightly.

By how much and if it matters significantly, i dont know, but it's probably
valve type dependent.

Why 6.3volts anyway?

Not a valve expert, but i would think:

a) each heater would draw more current.
b) valve reliability would go down.
c) valve transfer characteristics would change slightly.

By how much and if it matters significantly, i dont know, but it's probably
valve type dependent.

Why 6.3volts anyway?

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)

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)

On Sat, 13 Dec 2003 14:14:03 +0000, 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?

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).

--
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... :-)

On Sat, 13 Dec 2003 14:14:03 +0000, 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?

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).

--
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... :-)

"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.....