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

OT - A question for the valve experts.
 

"Dave Plowman" wrote in message
...
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?

Measure the voltages with an Avo 8........ if you are using a digital
multimeter the voltages will always read slightly higher than those
indicated on the circuit diagram..
Certainly with early valve circuits - good examples are Quad & Leak -
there was always a note on the bottom of the circuit diagrams to say that
all voltages shown (shewn) are measured with a voltmeter of 20,000 Ohms/Volt
sensitivity . Translated into English = measured with an Avo 8
multimeter.
In the particular case of your Sig Gen - I wouldn't worry

OT - A question for the valve experts.
 

"Dave Plowman" wrote in message
...
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?

Measure the voltages with an Avo 8........ if you are using a digital
multimeter the voltages will always read slightly higher than those
indicated on the circuit diagram..
Certainly with early valve circuits - good examples are Quad & Leak -
there was always a note on the bottom of the circuit diagrams to say that
all voltages shown (shewn) are measured with a voltmeter of 20,000 Ohms/Volt
sensitivity . Translated into English = measured with an Avo 8
multimeter.
In the particular case of your Sig Gen - I wouldn't worry

OT - A question for the valve experts.
 

In article , 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?

Is 500mA the load when in normal use?

I'd suggest using a series resistor if the 'in use' voltage is well above
6.3V. You may need to check the correct value while in use, though, as the
resistance of the heaters will be temperature dependent.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

OT - A question for the valve experts.
 

In article , 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?

Is 500mA the load when in normal use?

I'd suggest using a series resistor if the 'in use' voltage is well above
6.3V. You may need to check the correct value while in use, though, as the
resistance of the heaters will be temperature dependent.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html