series transformer primaries

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Raymond Koonce
Guest

Posted: Sun Jan 16, 2005 2:29 am Post subject: series transformer primaries

Hi RATs, I'm working on an amp for 230VAC power and it will have four filament transformers: two 5V 2A, one 5V 3A and one 6.3V 2A. Is it OK to connect two of the 120V primaries in series? Or would it be better to look for transformers with 230VAC primaries, not common in the US. TIA Raymond

Phil Allison
Guest

Posted: Sun Jan 16, 2005 3:18 am Post subject: Re: series transformer primaries

"Raymond Koonce"

Quote:

Hi RATs,

I'm working on an amp for 230VAC power and it will have four filament
transformers: two 5V 2A, one 5V 3A and one 6.3V 2A. Is it OK to connect
two of the 120V primaries in series? Or would it be better to look for
transformers with 230VAC primaries, not common in the US.

** If two *separate* AC supply transformers are to have their primaries
wired in series then the primary currents must match at all times when the
set up is in operation. This is certain if the units are identical and the
secondaries are wired in parallel. If the units are identical and the two
secondaries have identical loads then it will also work OK.

However, if the loads are two tube filaments, then there can be an imbalance
in load that will produce an imbalance in primary voltage. There will also
be gross imbalance if one tube is absent or the filament fails.

BTW

When you say "230 volt power" do you also mean 50 Hz frequency ? If so
then many transformers sold for use in the USA are inherently unsuitable,
they will "growl" audibly and seriously overheat on 50 Hz power.

................. Phil

mick
Guest

Posted: Sun Jan 16, 2005 3:24 am Post subject: Re: series transformer primaries

On Sat, 15 Jan 2005 15:29:50 -0600, Raymond Koonce wrote:

Quote:

The VA load of series transformers should be identical otherwise the
secondary voltage will vary. So, if your two 5V 2A transformers both have
120V primaries you can connect them in series because they are both 10VA
loads. You shouldn't connect 120v primaries on the other two in series
though as the VA ratings are 15VA and 12.6VA.

--
Mick
(no M$ software on here... :-) )
Web: http://www.nascom.info
Web: http://projectedsound.tk

Phil Allison
Guest

Posted: Sun Jan 16, 2005 4:35 am Post subject: Re: series transformer primaries

"mick"
Raymond Koonce wrote:

Quote:

** More than that the two transformers need to be identical - ie same
magnetising current, saturation voltage, regulation factor etc.

Quote:

So, if your two 5V 2A transformers both have 120V primaries you can
connect them in series because they are both 10VA loads.

** Huh ???? - you have mixed up rated load with actual laod.

Quote:

You shouldn't connect 120v primaries on the other two in series
though as the VA ratings are 15VA and 12.6VA.

** But if the actual load VAs were matched it might be OK.

However - the 50 Hz saturation thing is still a worry in all cases.

............... Phil

Raymond Koonce
Guest

Posted: Sun Jan 16, 2005 4:46 am Post subject: Re: series transformer primaries

Phil Allison wrote:

Quote:

"Raymond Koonce"

Hi RATs,

I'm working on an amp for 230VAC power and it will have four filament
transformers: two 5V 2A, one 5V 3A and one 6.3V 2A. Is it OK to connect
two of the 120V primaries in series? Or would it be better to look for
transformers with 230VAC primaries, not common in the US.

** If two *separate* AC supply transformers are to have their primaries
wired in series then the primary currents must match at all times when the
set up is in operation. This is certain if the units are identical and the
secondaries are wired in parallel. If the units are identical and the two
secondaries have identical loads then it will also work OK.

However, if the loads are two tube filaments, then there can be an imbalance
in load that will produce an imbalance in primary voltage. There will also
be gross imbalance if one tube is absent or the filament fails.

That's what I was afraid of. Just thought I'd ask.

Quote:

BTW

When you say "230 volt power" do you also mean 50 Hz frequency ? If so
then many transformers sold for use in the USA are inherently unsuitable,
they will "growl" audibly and seriously overheat on 50 Hz power.

Yes, I do mean 50Hz AC at 230V nominal. I have done OK at 50Hz with

US/Canadian transformers with universal 115/230 primaries, specifically
the Hammond 378CX, but I believe it is rated for 50/60Hz duty. I
understand that a 60Hz transformer will not perform at optimum on 50Hz
power.

Thanks for your input,

Raymond

Quote:

................ Phil

Raymond Koonce
Guest

Posted: Sun Jan 16, 2005 4:47 am Post subject: Re: series transformer primaries

mick wrote:

Quote:

On Sat, 15 Jan 2005 15:29:50 -0600, Raymond Koonce wrote:

Hi RATs,

I'm working on an amp for 230VAC power and it will have four filament
transformers: two 5V 2A, one 5V 3A and one 6.3V 2A. Is it OK to connect
two of the 120V primaries in series? Or would it be better to look for
transformers with 230VAC primaries, not common in the US.

The VA load of series transformers should be identical otherwise the
secondary voltage will vary. So, if your two 5V 2A transformers both have
120V primaries you can connect them in series because they are both 10VA
loads. You shouldn't connect 120v primaries on the other two in series
though as the VA ratings are 15VA and 12.6VA.

Hi Mick,

That's what I thought too, but I thought I'd run it past the experts.

Thanks,

Raymond

Patrick Turner
Guest

Posted: Sun Jan 16, 2005 6:38 am Post subject: Re: series transformer primaries

Raymond Koonce wrote:

Quote:

Phil Allison wrote:

"Raymond Koonce"

Hi RATs,

I'm working on an amp for 230VAC power and it will have four filament
transformers: two 5V 2A, one 5V 3A and one 6.3V 2A. Is it OK to connect
two of the 120V primaries in series? Or would it be better to look for
transformers with 230VAC primaries, not common in the US.

** If two *separate* AC supply transformers are to have their primaries
wired in series then the primary currents must match at all times when the
set up is in operation. This is certain if the units are identical and the
secondaries are wired in parallel. If the units are identical and the two
secondaries have identical loads then it will also work OK.

However, if the loads are two tube filaments, then there can be an imbalance
in load that will produce an imbalance in primary voltage. There will also
be gross imbalance if one tube is absent or the filament fails.

That's what I was afraid of. Just thought I'd ask.

BTW

When you say "230 volt power" do you also mean 50 Hz frequency ? If so
then many transformers sold for use in the USA are inherently unsuitable,
they will "growl" audibly and seriously overheat on 50 Hz power.

Yes, I do mean 50Hz AC at 230V nominal. I have done OK at 50Hz with
US/Canadian transformers with universal 115/230 primaries, specifically
the Hammond 378CX, but I believe it is rated for 50/60Hz duty. I
understand that a 60Hz transformer will not perform at optimum on 50Hz
power.

Thanks for your input,

Raymond

Power transformers from many commercial winders are
wound to place the Bmax at about 1.2 Tesla.

Something wound in the the US to suit 60 Hz will have a certain number
of turns per volt to produce the 1.2 Tesla magnetic field strength, and no more.

However, if the same voltage is applied to such a transformer but the F = 50 Hz,
the
Bmax would be pushed up to 1.2 x 60/50 = 1.44 Tesla, and the transformer iron is
then
beginning to saturate and the the magnetizing current increases a lot, and
becomes
non sinusoidal and the transformer "growls" as Phil says.
So to be able to run with 50 Hz the turns per volt must be increased 20%.

Transformers wound for 230v ie, with two 115v primaries that
can be seriesed for 230v, then it should be assumed they will be perhaps used
with 240v
as we have here in Oz, and often it meaures 250v, and its at 50 Hz,
so such transformers need about 30% more turns per volt than something
designed specifically for US conditions.

Radios sold in Oz used to have 260, 240, and 220v taps on the power tranny
so that if you lived in the regional areas at the end of a power line, you could
set
the radio for the lower voltage.
People would do that, and then move to the city, and the mains might then be
250v,
and the radio would then have 12% higher working voltages.
They mostly survived. Not many folks bothered to have their radios set to 220v at
the farm
so the voltages in the radio were all 10% low, so that favoured the radio's life.

A power tranny wound to suit Oz conditions with a pair of universal primary
windings each with enough taps to
to allow 100, 110, 120, 230, 240v at 50 Hz will run cooler and quieter in the US
with 60 Hz. when the right voltage is chosen.
It will also be usable in Japan or Europe or China.
Maybe India, I am not sure anout Indian power.

Much of what comes from China is suited to 220v and 50 Hz.
When its gets to Oz, we have 250v sometimes, and I have seen Jolida amps made in
china
blow their electrolytics and tubes up because the HT went from the designed 470v
to
an unwanted 530v, all because the makers and the US joint venture controlling
entrepreneur were lame brained.

Patrick Turner.

robert casey
Guest

Posted: Sun Jan 16, 2005 8:02 am Post subject: Re: series transformer primaries

Raymond Koonce wrote:

Quote:

Hi RATs,

I'm working on an amp for 230VAC power and it will have four filament
transformers: two 5V 2A, one 5V 3A and one 6.3V 2A. Is it OK to
connect two of the 120V primaries in series? Or would it be better to
look for transformers with 230VAC primaries, not common in the US.

As mentioned by others, unequal loading will not split the
230VAC equally. And also transforemrs designed for 60Hz
may go into core saturation if run at the same voltage at
50Hz. However, a 60Hz 125V transformer can run at 104V at
50Hz without the core saturation problem. It's 6.3V will
yield 5.2V so that would run the 5V tubes. If you have a
voltage converter autoformer designed for supplying
100V AC power to Japanese domestic equipment (their powerline
is 100VAC, northern Japan on 50Hz, southern Japan 60Hz, I
don't know why) you could get the 100V. But at this point
you might as well get the 230V filament transformers rather
than mess around with this....

Tim Williams
Guest

Posted: Sun Jan 16, 2005 8:26 am Post subject: Re: series transformer primaries

"Raymond Koonce" <rkoonce@tyler.net> wrote in message
news:10uj2r03nu8p01b@corp.supernews.com...

Quote:

I'm working on an amp for 230VAC power and it will have four filament
transformers: two 5V 2A, one 5V 3A and one 6.3V 2A. Is it OK to
connect two of the 120V primaries in series? Or would it be better to
look for transformers with 230VAC primaries, not common in the US.

Only if they have the same VA load (actual load, not rating) and hence the
same primary current. Otherwise, voltage and current will distribute
themselves as two filaments, say 100V and 140V, in series, as seen on the
primary side; or likewise, a 10VAC supply feeding 4V and 6V filaments on the
secondary side. Same equivalent circuit, given a reasonably ideal
transformer (yes).

Or you can ensure the same secondary voltage by paralleling the windings.
Load sharing between them is not a concern here because the primary currents
are convieniently equal. Such a series-parallel wiring is actually the only
safe and "solid" way to connect two transformers (both windings in series
isn't "solid", while both windings in parallel causes inevitable load
sharing, shorted turns and excessive heating).

That assumes they aren't on opposite ends of the B supply or something, of
course, and can be freely paralleled. ;)

Assuming your transformers are loaded as given above, your best luck would
be the 5V 3A and 6.3V 2A primaries in series. If you could parallel the 5V
2A and 5V 3A windings (I'm guessing 300B and 5U4, so no), they would share
the load equally due to equal Ip, leaving one slightly overloaded and the
other slightly under (2.5A each for a total of 5A specified).

Obviously you can't parallel the 6.3V and 5V windings for a similar
stabilization, unless you happen to have a 5:6.3V transformer on hand.

That still leaves an odd man out, so look into 230V primaries (perhaps CT
primary (115/230) or true dual types as seen in most supply catalogs e.g.
Mouser), or at worst, an isolation or autotransformer.

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

mick
Guest

Posted: Mon Jan 17, 2005 1:09 am Post subject: Re: series transformer primaries

On Sun, 16 Jan 2005 10:35:13 +1100, Phil Allison wrote:

<snip>

Quote:

** More than that the two transformers need to be identical - ie same
magnetising current, saturation voltage, regulation factor etc.

So, if your two 5V 2A transformers both have 120V primaries you can
connect them in series because they are both 10VA loads.

** Huh ???? - you have mixed up rated load with actual laod.

You shouldn't connect 120v primaries on the other two in series
though as the VA ratings are 15VA and 12.6VA.

** But if the actual load VAs were matched it might be OK.

However - the 50 Hz saturation thing is still a worry in all cases.

Correct on all points Phil. Sorry, I didn't have my thinking head on! :-)

--
Mick
(no M$ software on here... :-) )
Web: http://www.nascom.info
Web: http://projectedsound.tk

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