I have a stupid question about transformers.

Why don't people use ferrite cores for audio output transformers?

--
Fred Gilham
America does not know the difference between sex and money. It treats
sex like money because it treats sex as a medium of exchange, and it
treats money like sex because it expects its money to get pregnant and
reproduce. --- Peter Kreeft

Aren't toroids wound on ferrite material?

From: Fred Gilham
Newsgroups: rec.audio.tubes
Date: 15 Jan 2004 17:15:13 -0800
Subject: Stupid transformer question


I have a stupid question about transformers.

Why don't people use ferrite cores for audio output transformers?

--
Fred Gilham
America does not know the difference between sex and money. It treats
sex like money because it treats sex as a medium of exchange, and it
treats money like sex because it expects its money to get pregnant and
reproduce. --- Peter Kreeft

"Fred Gilham"

I have a stupid question about transformers.

Why don't people use ferrite cores for audio output transformers?


** It would be very expensive and make them far too big.

Ferrite saturates magnetically at much lower levels than iron.




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

"Jon Yaeger"

Aren't toroids wound on ferrite material?


** Ones for high frequencies are.

AC supply toroids use a continuous wound strip of grain oriented
silicon steel (aka GOSS).





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

Fred Gilham wrote:

I have a stupid question about transformers.

Why don't people use ferrite cores for audio output transformers?

People want their audio transformers to have a large amount of inductance
at low frequency.
If you didn't have a core at all the inductance would be approximately
constant at all frequencies, but it might only be 100 mH which
would cause a serious shunting of LF, since 30mH
is only 31.4 ohms at 50 Hz.
But at 20 kHz, the winding impedance is 12.56k ohms,
and the inductance is sufficient to prevent load shunting,
so an iron core is not needed as F rises.
Using an iron core of some kind raises the amount of inductance of the
coil,
depending on the U of the iron, which is unacceptably low for ferrite
at LF, although still well above an air cored coil which has a U =1.0.
When iron is used, the U might be between 1.0 and many thousand, since the
iron raises
inductance by that much.
Ferrite, like many different magnetic materials has a different U
for different frequencies, and what we want for AF transformers
is something with a U of several thousand at 50 Hz,
so that a transformer's primary winding inductive reactance does not
shunt the load and tube plate resistance, hence the need
for 100H in a typical good quality OPT at low levels of operation.
The ability of the magnetic core to increase its inductance
over that of air varies with frequency AND the applied voltage across
the coil.
Grain oriented silicon steel is one of the better materials for AF
transformers
because its U at 50 Hz might be 40,000, depending on the manufacturer,
the magnetic field strength, ( B in Tesla ), and the frequency of
operation, and thickness of
lamination material.
But all iron based laminated sheet meatl core materials have a point where
saturation is reached at
some B, usually between 1 and 1.5 Tesla, and enough turns are
needed for a given core cross sectional area to make the B = or under 0.3
Tesla
at 50 Hz, at maximum applied voltage level, ie voltage clipping
of the amp.
With silicon steel cores, even those low U cores without
the rolling and heat treatment to orient the grain, the amount of
inductance
is usually sufficient if the B = 0.3T or less at 50 Hz at clipping.
It means that at 12.5 Hz, B = 1.2 T, and indeed you will see
saturation distortion at near clipping input voltage at 12.5 Hz.

A mains transformer might be constructed to "run at 1.2 Tesla"
at 50 Hz, and it is near saturation, but toroidal GOSS core
will exhibit a high amount of inductance, so magnetisong current through
the winding is very low.
This mains transformer will have 1/4 of the turns of the audio trannie's
primary which will run at 12.5 Hz at 1.2T.
Thus the mains tranny is useless for F below 50 Hz at full power,
but it will have less power wasted in the windings, because a lower
turn/volt is used.

In a conventional E&I core where non oriented silicon steel
is used, the magnetising current might be far higher, because U is lower,
and inductance is lower, so magnetising current is far higher,
and indeed the core heats up, even without any load connected.

T cut a long story short, GOSS are the cheapest and best cores
for most folks for audio use,
and also for mains power trannies.
Toroidal cores offere the least losses for a given B.
But it is possible to get excellent low distortion
and low loss results from E&I
"wasteless pattern" laminations, also using GOSS.


The subject of core materials takes more explaining than I have room for,
perhaps you could visit
http://www.acs.comcen.com.au/ferrites.html

This should provoke the questions like "WTF is magnetism anyway?",
and then you need to go to other sites or books to answer all that,
and then to another lot of books or websites to answere even more
questions,
and so on....

Patrick Turner.




--
Fred Gilham
America does not know the difference between sex and money. It treats
sex like money because it treats sex as a medium of exchange, and it
treats money like sex because it expects its money to get pregnant and
reproduce. --- Peter Kreeft

Behold, Jon Yaeger signalled from keyed 4-1000A filament:

Aren't toroids wound on ferrite material?

Audio toroids? Nope!

From: Fred Gilham Newsgroups:
rec.audio.tubes
Date: 15 Jan 2004 17:15:13 -0800
Subject: Stupid transformer question


I have a stupid question about transformers.

Why don't people use ferrite cores for audio output transformers?

Not a stupid question at all :-)

Permeability and LF bandwidth. Ferrite is really crummy at low audio
frequencies and saturates too easily. Also, to acheive the same
permeability of iron, you'd need a HUGE core.

--
Gregg
*It's probably useful, even if it can't be SPICE'd*
http://geek.scorpiorising.ca

On Fri, 16 Jan 2004 14:49:04 +1100, Patrick Turner wrote:



Fred Gilham wrote:

I have a stupid question about transformers.

Why don't people use ferrite cores for audio output transformers?


snip

A mains transformer might be constructed to "run at 1.2 Tesla" at 50 Hz,
and it is near saturation, but toroidal GOSS core will exhibit a high
amount of inductance, so magnetisong current through the winding is very
low.
This mains transformer will have 1/4 of the turns of the audio trannie's
primary which will run at 12.5 Hz at 1.2T. Thus the mains tranny is
useless for F below 50 Hz at full power, but it will have less power
wasted in the windings, because a lower turn/volt is used.

snip


Thanks for that lot, Patrick. I had been wondering about using a
torroidal mains transformer as a p-p output tranny, choosing a suitable
ratio and using the split primary as the 2 halves of the p-p primary
winding. I suspected that bass would be lacking, but using smallish
sealed-box speakers it may be acceptable. For experimentation on a tight
budget it might be worth trying. It would be interesting to see a response
curve for a mains tranny used that way.

--
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... :-)

"Form@C"


Thanks for that lot, Patrick. I had been wondering about using a
toroidal mains transformer as a p-p output tranny, choosing a suitable
ratio and using the split primary as the 2 halves of the p-p primary
winding.

** Perfectly doable.


I suspected that bass would be lacking, but using smallish
sealed-box speakers it may be acceptable.


** No need for that - depending on your design.


For experimentation on a tight
budget it might be worth trying. It would be interesting to see a response
curve for a mains tranny used that way.


** I can tell you now - flat from a few Hz to at least 60 kHz at the -
3 dB point. What you really need is a toroid with two identical 240 volt
rated primaries - plus a suitable low voltage winding. Any toroidal maker
can do one as a special job and way cheaper than the usual E cores.

The only drawback is the need for *exact * DC current balance in the
primaries.






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

"Form@C" wrote:

On Fri, 16 Jan 2004 14:49:04 +1100, Patrick Turner wrote:



Fred Gilham wrote:

I have a stupid question about transformers.

Why don't people use ferrite cores for audio output transformers?


snip

A mains transformer might be constructed to "run at 1.2 Tesla" at 50 Hz,
and it is near saturation, but toroidal GOSS core will exhibit a high
amount of inductance, so magnetisong current through the winding is very
low.
This mains transformer will have 1/4 of the turns of the audio trannie's
primary which will run at 12.5 Hz at 1.2T. Thus the mains tranny is
useless for F below 50 Hz at full power, but it will have less power
wasted in the windings, because a lower turn/volt is used.

snip

Thanks for that lot, Patrick. I had been wondering about using a
torroidal mains transformer as a p-p output tranny, choosing a suitable
ratio and using the split primary as the 2 halves of the p-p primary
winding. I suspected that bass would be lacking, but using smallish
sealed-box speakers it may be acceptable. For experimentation on a tight
budget it might be worth trying. It would be interesting to see a response
curve for a mains tranny used that way.

The response for a mains toroidal is surprisingly wide,
anything from a few Hz to maybe 100 kHz.

Suppose you had a P of 240v to 2 x 20v S.
The 20v could be paralleled, so you'd have a 240:20 turn ratio
which is 12 :1 which is a bit low for most tube applications unless
you use low impedance tubes, like 6AS7G.
12:1 turn ratio is 144:1 Z ratio, which means you'd have 1,152 ohms to 8 ohms,

which means that to get a match, you'd need say 4 x EL34 all paralleled
for a class A SE amp.
To keep the DC out of the tranny because you have no CT, you coulod have a
large choke to supply DC to the tubes,
and cap couple the OPT, and you would get about 35 w into 1152 ohms, which is
200vrms on the primary, and unfortunately, the core would saturate at about
35 Hz, because at the normal 240v across the primary,
the B would be about 1.2T at 50 Hz, and we really want about 3 times the
primary turns to give
an ideal bass response.

Using the mains tranny in a circlotron design with 4 x EL34 is also possible,
as the DC flow is about the same in both directions across the P winding,
and thus there is no need for a choke feed.
Inbalance and poor bass capability are still present.
To do any better, the tubes should be say 4 x 6AS7G, which
could make about 25 watts class AB, perhaps with a lower turn ratio.

Not many mains toroidals have two identical 240v windings,
and a set of secondaries.

BUT, if you could find a toroidal 1:1 240v isolation tranny,
it may be possible to wind on some secondaries over the primaries,
but this still isn't ideal because there are still not enough turns to allow
low bass at full power with KT88,EL34,6L6 type of tubes,
and the two P halves of the winding have asymetric leakage inductance
to the wound on low voltage winding.

So, to cut a long story short, the circlotron with 6AS7G is
about the simplest, although you need a decent driver amp to make
at least 150vrms to power each of the 6AS7G grids, because the
circlotron has 1/2 the total primary signal appearing at its anode and
cathode.

I would have latched onto the idea of using mains trannies for audio
if I could get a decent load match, and low thd down to 20 Hz at full power.

But to do any good with mains toroidal trannies, the best devices are
mosfets and transistors.
Then its a different ball game, and a 500VA toroidal core
can easily be set up with about 300 turns of 2mm thick wire, which the DIY
person
can do reasonably easily, and the tranny run as an auto transformer for
a wide range of output impedance matches, and the devices can run in class A,
so that with 4 x npn mosfets, with 25 watts disipated in each,
and with about a 35v supply, about 45 watts of class A power is avaialble.
That's a whole other story.

But if one started with a toriod core, say a nice big 500VA size,
then it is possible to wind your own, but you will need around
2,000 P turns to get low bass.
This can be wound on in two 1,000 turn sections,
with mylar insulation tape wound between layers in the section.
This stops wires which cross each other from biting into each other,
and causing a shorted turn,
The S sections are wound between the two 1,000 turn sections, and use
much thicker wire, and the sections paralleled.
The wire can be first wound onto a peice of broom handle about 1 turn long,
which makes a shuttle, and the wire is passed onto the core one turn after
another,
and believe you me, it takes forever, because I have rewound a couple of
toroids for mains use to make them quieter, because most makers
don't use enough turns for hi-fi applications, and they don't
vacuum impregnate the wound transformer.
I really don't like toroids at all for OPT, because with so many taps and
windings,
it is hard to do, and I use normal E&I lams of GOSS, with neat layer winding
layers,
and I interleave say 5P x 4S for about at least 80 kHz of BW,
or in the case of 6S x 5P, 300 kHz is readily available.

By the time one has tried to achieve something ideal with a mains tranny,
one may find it would have been better to go to Sowter, or Hammond,
or any of many higher quality items which are available off the shelf.
My solution was that I just made a winding lathe to be independant from having
to use
expensive ready made or handcrafted OPTs.
After about 3 attempts, the trannies performed better than any commercial
product I have
ever tested.
Basic details are at my website.
But it really takes enormous dedication to wind your own OPTs.
Its easy to wind something that might produce smoke in a year's time, or
sooner.

Its possible to use a mains tranny where low bass isn't needed,
and use some other amp for low bass, say something solid state.

In such a case, it'd be best to make sure the amp has an input filter to
limit input of low bass, so an LF cut off at say 100Hz might be about right,
and let a sub woofer do the below bit.
Personally, I don't like subs, but feel free to experiment.

Patrick Turner.



--
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... :-)

"Patrick Turner"


The response for a mains toroidal is surprisingly wide,
anything from a few Hz to maybe 100 kHz.


** That's what I said already - you asshole.



Suppose you had a P of 240v to 2 x 20v S.
The 20v could be paralleled, so you'd have a 240:20 turn ratio
which is 12 :1 which is a bit low for most tube applications unless
you use low impedance tubes, like 6AS7G.
12:1 turn ratio is 144:1 Z ratio, which means you'd have 1,152 ohms to 8
ohms,



** Suppose the Turneroid was not an asshole - then he might not post so
much stinking ****e.



which means that to get a match, you'd need say 4 x EL34 all paralleled
for a class A SE amp.
To keep the DC out of the tranny because you have no CT, you coulod have a
large choke to supply DC to the tubes,
and cap couple the OPT, and you would get about 35 w into 1152 ohms, which
is
200vrms on the primary, and unfortunately, the core would saturate at about
35 Hz, because at the normal 240v across the primary,
the B would be about 1.2T at 50 Hz, and we really want about 3 times the
primary turns to give
an ideal bass response.


** Suppose the earth was flat - the the Turneroid would be an expert on
curved surfaces.



Using the mains tranny in a circlotron design with 4 x EL34 is also
possible,
as the DC flow is about the same in both directions across the P winding,
and thus there is no need for a choke feed.


** Suppose the Turneroid were to choke - then there is no more need to
feed him too.



Inbalance and poor bass capability are still present.
To do any better, the tubes should be say 4 x 6AS7G, which
could make about 25 watts class AB, perhaps with a lower turn ratio.

Not many mains toroidals have two identical 240v windings,
and a set of secondaries.


** The Turneroid is such an utter ****WIT !!!

Custom toriods are available from any winder at low cost !!!!!



BUT, if you could find a toroidal 1:1 240v isolation tranny,


** If you could find the tooth fairy ..........



it may be possible to wind on some secondaries over the primaries,
but this still isn't ideal because there are still not enough turns to allow
low bass at full power with KT88,EL34,6L6 type of tubes,
and the two P halves of the winding have asymetric leakage inductance
to the wound on low voltage winding.

So, to cut a long story short,


** Simply shoot the Turneroid.

Amen.




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

On Sat, 17 Jan 2004 00:58:33 +1100, Patrick Turner wrote:

snip

Suppose you had a P of 240v to 2 x 20v S. The 20v could be paralleled, so
you'd have a 240:20 turn ratio which is 12 :1 which is a bit low for most
tube applications unless you use low impedance tubes, like 6AS7G. 12:1
turn ratio is 144:1 Z ratio, which means you'd have 1,152 ohms to 8 ohms,

snip


Around here I can get 115+115v:9+9v 30VA, which I work out to be
5224.7R:8R if I parallel the secondaries, which would be just about ideal
for a pair of 6L6s in p-p. Providing the two primaries are sufficiently
similar, of course. I haven't tested any, but I would assume that they
would be pretty close as the primaries (and secondaries for that matter)
are specified to be parallelled under normal use, and any mismatch would
cause heating. I suppose that any dc imbalance could be corrected by using
a low value resistor in series with one winding to even them up. Using a
p-p output stage gets rid of a lot of the dc problem of course. The 30VA
size should normally pass somewhere around 130mA when used as a
mains tranny, so the wire size (at least) should be happy with the
70-100mA of a 6L6. Once again, this is educated guesswork on my part, the
primary may saturate at a frequency too high to be useful.

--
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... :-)

Thanks to everyone for all the helpful information.

--
Fred Gilham
When trying to reach the lowest common denominator, you have to be
prepared for the occasional division by zero.

On Fri, 16 Jan 2004 07:50:36 -0800, Fred Gilham wrote:


Thanks to everyone for all the helpful information.


Sorry for hijacking your thread a bit, Fred, but this is getting
interesting! :-)

--
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... :-)

Sorry for hijacking your thread a bit, Fred, but this is getting
interesting! :-)

No problem! It is indeed interesting.

--
Fred Gilham
An ABC camera crew interviewed Hillary Clinton in the Bahamas, where
she was sunning herself on a flat rock to keep her body temperature
up. "Cookies," she said, eyeing the cameras. "Children." -- Fred Reed

"Form@C"


Around here I can get 115+115v:9+9v 30VA, which I work out to be
5224.7R:8R if I parallel the secondaries, which would be just about ideal
for a pair of 6L6s in p-p.


** No way.

115 volts AC ( or 322 volts peak to peak ) is the core saturation voltage
at 50 Hz.

The plate of the 6L6 will swing over a 640 volt range with a 400 volt
supply - so a twin 240 volt tranny is needed even to get 50 Hz at full
power.


I suppose that any dc imbalance could be corrected by using
a low value resistor in series with one winding to even them up.


** How stupid.

The DC imbalance is in the tubes - not the tranny.



Using a p-p output stage gets rid of a lot of the dc problem of course.


** That was assumed to be the case.


The 30VA
size should normally pass somewhere around 130mA when used as a
mains tranny, so the wire size (at least) should be happy with the
70-100mA of a 6L6.


** The toroidal core has NO AIR GAP !!!

Even a few mA of DC imbalance will push it into saturation.


Once again, this is educated guesswork on my part, the
primary may saturate at a frequency too high to be useful.


** For a pair of EL84s with a 300 volt supply a 30 VA toroid with two
*240 volt* windings would be fine.




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

On Sat, 17 Jan 2004 10:06:05 +1100, Phil Allison wrote:


"Form@C"


Around here I can get 115+115v:9+9v 30VA, which I work out to be
5224.7R:8R if I parallel the secondaries, which would be just about
ideal for a pair of 6L6s in p-p.


** No way.

115 volts AC ( or 322 volts peak to peak ) is the core saturation
voltage
at 50 Hz.

The plate of the 6L6 will swing over a 640 volt range with a 400 volt
supply - so a twin 240 volt tranny is needed even to get 50 Hz at full
power.


As it happens, I can't get a 400v supply on the 6L6s (I want to run them
as triodes and the screen voltage limit is 250v max). I see your point
though.


I suppose that any dc imbalance could be corrected by using
a low value resistor in series with one winding to even them up.


** How stupid.

The DC imbalance is in the tubes - not the tranny.


No, just mistaken. I had assumed that we were talking about winding
resistance or impedance imbalance here, due to winding the two primaries
as seperate windings rather than bifilar. My idea was to make up any
differences in load - not the valves (which I assumed would be close to
balanced). Perhaps if you had read the following sentences that would have
been clearer to you. Once again, I see your point now, but it should be
possible to balance the valves using the bias, surely? Many p-p OPTs are
ungapped so suffer from exactly the same problem. Their cores are also
carrying dc but don't saturate as the net flux is zero - or close to it. I
realise that balance would be more critical in this instance because the
transformer is running much closer to saturation than a "proper" OPT.


snip

** For a pair of EL84s with a 300 volt supply a 30 VA toroid with two
*240 volt* windings would be fine.



Thanks Phil.


--
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... :-)

"Form@C"


I suppose that any dc imbalance could be corrected by using
a low value resistor in series with one winding to even them up.


** How stupid.

The DC imbalance is in the tubes - not the tranny.


No, just mistaken. I had assumed that we were talking about winding
resistance or impedance imbalance here, due to winding the two primaries
as separate windings rather than bifilar.


** Quote:

"The only drawback is the need for *exact * DC current balance in the
primaries."

How can you possibly misread THAT !!!!!!



My idea was to make up any
differences in load - not the valves (which I assumed would be close to
balanced).


** Then you do not know much about valves.


Perhaps if you had read the following sentences that would have
been clearer to you.


** The error you made was very clear.


Once again, I see your point now, but it should be
possible to balance the valves using the bias, surely?


** Sure - then they drift out of balance.


Many p-p OPTs are ungapped so suffer from exactly the same problem.


** Only toroids have "NO AIR GAP ".

Only toroids saturate with "a few mA of DC imbalance"

All E-core trannies ***have gaps*** - between each E and I lamination.



Their cores are also carrying dc but don't saturate as the net flux is
zero - or close to it. I
realise that balance would be more critical in this instance because the
transformer is running much closer to saturation than a "proper" OPT.


** You are wrong again.

If the primary is wound with enough turns to avoid core saturation at 20
Hz then the sensitivity to DC imbalance gets WORSE !!!!

PP tube amps that use toroidal OTs also usually have servo bias balancing
systems - or owners prepared to do the same manually on a regular basis.




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

Phil Allison wrote:

"Patrick Turner"

The response for a mains toroidal is surprisingly wide,
anything from a few Hz to maybe 100 kHz.

** That's what I said already - you asshole.

Suppose you had a P of 240v to 2 x 20v S.
The 20v could be paralleled, so you'd have a 240:20 turn ratio
which is 12 :1 which is a bit low for most tube applications unless
you use low impedance tubes, like 6AS7G.
12:1 turn ratio is 144:1 Z ratio, which means you'd have 1,152 ohms to 8
ohms,

** Suppose the Turneroid was not an asshole - then he might not post so
much stinking ****e.

which means that to get a match, you'd need say 4 x EL34 all paralleled
for a class A SE amp.
To keep the DC out of the tranny because you have no CT, you coulod have a
large choke to supply DC to the tubes,
and cap couple the OPT, and you would get about 35 w into 1152 ohms, which
is
200vrms on the primary, and unfortunately, the core would saturate at about
35 Hz, because at the normal 240v across the primary,
the B would be about 1.2T at 50 Hz, and we really want about 3 times the
primary turns to give
an ideal bass response.

** Suppose the earth was flat - the the Turneroid would be an expert on
curved surfaces.

I always thought the earth rested on the saddle point of
a hyperbolic paraboloid? (x^2/a^2) - (y^2/b^2) = z
JLS

Using the mains tranny in a circlotron design with 4 x EL34 is also
possible,
as the DC flow is about the same in both directions across the P winding,
and thus there is no need for a choke feed.

** Suppose the Turneroid were to choke - then there is no more need to
feed him too.

Inbalance and poor bass capability are still present.
To do any better, the tubes should be say 4 x 6AS7G, which
could make about 25 watts class AB, perhaps with a lower turn ratio.

Not many mains toroidals have two identical 240v windings,
and a set of secondaries.

** The Turneroid is such an utter ****WIT !!!

Custom toriods are available from any winder at low cost !!!!!

BUT, if you could find a toroidal 1:1 240v isolation tranny,

** If you could find the tooth fairy ..........

it may be possible to wind on some secondaries over the primaries,
but this still isn't ideal because there are still not enough turns to allow
low bass at full power with KT88,EL34,6L6 type of tubes,
and the two P halves of the winding have asymetric leakage inductance
to the wound on low voltage winding.

So, to cut a long story short,

** Simply shoot the Turneroid.

Amen.

.......... Phil

"Form@C" wrote:

On Sat, 17 Jan 2004 00:58:33 +1100, Patrick Turner wrote:

snip

Suppose you had a P of 240v to 2 x 20v S. The 20v could be paralleled, so
you'd have a 240:20 turn ratio which is 12 :1 which is a bit low for most
tube applications unless you use low impedance tubes, like 6AS7G. 12:1
turn ratio is 144:1 Z ratio, which means you'd have 1,152 ohms to 8 ohms,

snip

Around here I can get 115+115v:9+9v 30VA, which I work out to be
5224.7R:8R if I parallel the secondaries, which would be just about ideal
for a pair of 6L6s in p-p.

The turn ratio is 230:9, ie,25.5:1, Z ratio = 653:1,
which means 5.2k to 8.
30w into 5.2k is 394 vrms a-a.
The mains tranny has been wound for a B = 1.2T at 230v
for the two seriesed windings at 60 Hz.
With 394v a-a, 1.2T would occur at 103 Hz,
and saturaturation at around 80 Hz, but for hi-fi
we want saturation at 14 Hz, so the mains tranny is quite hopeless
unless we limited the Vaa to around 70vrms.

Mains trannies will give a very very dissapointing bass response,
and something like 4 times the turns is required.

Providing the two primaries are sufficiently
similar, of course. I haven't tested any, but I would assume that they
would be pretty close as the primaries (and secondaries for that matter)
are specified to be parallelled under normal use, and any mismatch would
cause heating. I suppose that any dc imbalance could be corrected by using
a low value resistor in series with one winding to even them up. Using a
p-p output stage gets rid of a lot of the dc problem of course. The 30VA
size should normally pass somewhere around 130mA when used as a
mains tranny, so the wire size (at least) should be happy with the
70-100mA of a 6L6. Once again, this is educated guesswork on my part, the
primary may saturate at a frequency too high to be useful.

Indeed it will saturate at too high a F.

The DC balance in the PP core is also somewhat critical with a high U material
like strip wound GOSS, and E&I lams are far more forgiving in this regard.
C-cores with a very small air gap are even better.

Almost anything is better than a mains toroidal tranny for
a PP circuit.

That insulting poster, Mr Allison, said custom wound toroidals
are cheap to have wound to order.
Unfortunately, I have not found this to be the case, and getting the average
mains tranny winder to wind a decent toroidal OPT for a pair of 6L6
is all too much for them.
Last time I asked Tortech in Sydney to wind a toroidal to my spec,
they said it couldn't be done, and they had no alternatives to offer,
and the price was horrendous.

Last time I tried Harbuch, they wanted over aud $1,600
for 2 x PP OPTs and a choke and a mains tranny for EL34.
Not even any GOSS cores.
They were not interested in winding mains trannies which run at 0.85 Tesla,
which are then quiet enough to use in hi-fi gear.
The toroids I have re-wound to make them quiet originated from them.

I have long since given up having ppl custom wind any trannies for
my amplifiers in Oz because they are all much more expensive than imported
Hammond or Sowter.


I just wind all my own, to avoid the BS when dealing with folks
who really don't have a clue.

Patrick Turner.

--
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... :-)

"Patrick Turner"


The turn ratio is 230:9, ie,25.5:1, Z ratio = 653:1,
which means 5.2k to 8.
30w into 5.2k is 394 vrms a-a.
The mains tranny has been wound for a B = 1.2T at 230v
for the two seriesed windings at 60 Hz.


** Error #1 - any split primary ( 2 x 120 volt) tranny is made for 50
Hz operation.


With 394v a-a, 1.2T would occur at 103 Hz,
and saturaturation at around 80 Hz,


** Error # 2 - the real figures are 86 Hz and 68 Hz.


but for hi-fi we want saturation at 14 Hz,


** Error #4 - insane Turneroid figure plucked from his arse.


so the mains tranny is quite hopeless
unless we limited the Vaa to around 70vrms.


** Error #5 - the tranny just needs to be a twin 240 type.


Mains trannies will give a very very dissapointing bass response,
and something like 4 times the turns is required.


** Error #6 - follows from errors 1 through 5.


Almost anything is better than a mains toroidal tranny for
a PP circuit.


** Error #7 - follows from all other errors combined.



That insulting poster, Mr Allison, said custom wound toroidals
are cheap to have wound to order.


** Had it done many times - about 15 - 20 % extra on stock line prices
for the same VA.



Unfortunately, I have not found this to be the case, and getting the
average
mains tranny winder to wind a decent toroidal OPT for a pair of 6L6
is all too much for them.


** I know folk that have had this done by winders ( Harbuch) with no
problems or high cost.


Last time I asked Tortech in Sydney to wind a toroidal to my spec,
they said it couldn't be done,


** Error # 8 - Tortech recognised a lunatic spec and lunatic person
when the Turneroid approached.



Last time I tried Harbuch, they wanted over aud $1,600
for 2 x PP OPTs and a choke and a mains tranny for EL34.
Not even any GOSS cores.


** Error #9 - all toroidal cores are GOSS.

( The Turneroid dishonestly fails to mention he has changed topic.)



I have long since given up having ppl custom wind any trannies for
my amplifiers in Oz because they are all much more expensive than imported
Hammond or Sowter.


** Error #10 - again not talking about toroidals.



I just wind all my own,


** But not toroids.


to avoid the BS when dealing with folks who really don't have a clue.



** Nor do they pretend to be experts on tube amp transformer design.

They make mains transformers and line voltage audio outputs.




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

On Sat, 17 Jan 2004 17:55:37 +1100, Patrick Turner wrote:


snip

The turn ratio is 230:9, ie,25.5:1, Z ratio = 653:1, which means 5.2k to
8.
30w into 5.2k is 394 vrms a-a.
The mains tranny has been wound for a B = 1.2T at 230v for the two
seriesed windings at 60 Hz. With 394v a-a, 1.2T would occur at 103 Hz,
and saturaturation at around 80 Hz, but for hi-fi we want saturation at 14
Hz, so the mains tranny is quite hopeless unless we limited the Vaa to
around 70vrms.

Mains trannies will give a very very dissapointing bass response, and
something like 4 times the turns is required.

snip


Thanks Patrick. As you can tell, I'm no transformer expert! Your comments
have been very helpful indeed.


snip

That insulting poster, Mr Allison, said custom wound toroidals are cheap
to have wound to order.
Unfortunately, I have not found this to be the case, and getting the
average mains tranny winder to wind a decent toroidal OPT for a pair of
6L6 is all too much for them.
snip


I'll ask around here (We use a couple of winding firms at work for
custom transformers), but I suspect that the price will be prohibitive. I
don't think either of them winds audio trannies anyway so I would have to
be pretty specific. They wouldn't come with a performance guarantee either!

I was once told by one company that they buy in torroids with pre-wound
primaries and just wind secondaries onto them. We don't use that company
now!


--
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, 17 Jan 2004 18:20:04 +1100, Phil Allison wrote:


"Patrick Turner"


The turn ratio is 230:9, ie,25.5:1, Z ratio = 653:1, which means 5.2k to
8.
30w into 5.2k is 394 vrms a-a.
The mains tranny has been wound for a B = 1.2T at 230v for the two
seriesed windings at 60 Hz.


** Error #1 - any split primary ( 2 x 120 volt) tranny is made for
50 Hz operation.


Is it? That's interesting. I would have thought that 110+110 or 120+120
would have been intended for the american market and 60Hz, wheras a
115+115 would have been european and 50Hz. I would guess that most of
them design for 55Hz now and split the difference so that they can sell
to both markets! You may well be right though.


With 394v a-a, 1.2T would occur at 103 Hz, and saturaturation at
around 80 Hz,


** Error # 2 - the real figures are 86 Hz and 68 Hz.



In either case that isn't good! I can't comment on the validity of
the figures simply because I don't know (yet) how to work this out. It
does tie in with my original idea of using them with smallish infinite
baffle speakers though. I'm not likely to get a lot of output from the
speakers at the bass end. They are about -4dB at 85Hz at best.

You *know* I'm not an expert on transformers - I wouldn't be having this
discussion if I was! Also, I've learned more "tube" (horrible name - so
misleading and undescriptive!) theory since Christmas than I collected
over the last 30-odd years. Please have patience - I'm learning!


snip

so the mains tranny is quite hopeless
unless we limited the Vaa to around 70vrms.


** Error #5 - the tranny just needs to be a twin 240 type.



As I pointed out to Patrick though, that means a custom winding and it may
not be economically feasible. Even something like 240/110+110 isolating
tranny is almost certain to be a special order on an oversized core (to
fit the turns on - it would be a "site isolating transformer" for power
tools but without the encapsulation and box). We don't have a big choice
at the cheap end! Its probably as cheap to go to Sowter - and that's ruled
out on cost basis at the moment...


--
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... :-)

"Form@C"

Phil Allison wrote:


** Error #1 - any split primary ( 2 x 120 volt) tranny is made
for
50 Hz operation.


Is it? That's interesting. I would have thought that 110+110 or 120+120
would have been intended for the american market and 60Hz,


** How so - there are no 240 volt GPOs in the USA.


wheras a 115+115 would have been european and 50Hz.


** Spit primaries are for dual voltage operation - means USA or Europe.

USA power is nominally 117 volts 60Hz. 115 and 120 are just
approximations.




** Error #5 - the tranny just needs to be a twin 240 type.

As I pointed out to Patrick though, that means a custom winding and it may
not be economically feasible.


** Those who do not know need to find out.

NOT MAKE ****ING STUPID ASSUMPTIONS !!!!!!!!!!!!


Even something like 240/110+110 isolating
tranny is almost certain to be a special order on an oversized core .....


** Rot. Toroidal makers have numerpous cores in stock with primaries
already wound - just waiting for customers to order the secondary windings
they need. There is no need to adjust the core size for different voltages
since the primary always occupies under half the available space.




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

"Form@C" wrote in message
news

Thanks Patrick. As you can tell, I'm no transformer expert! Your comments
have been very helpful indeed.


** It is all a load of ****ing ****e - forget the stupid arsehole.



I'll ask around here (We use a couple of winding firms at work for
custom transformers), but I suspect that the price will be prohibitive.


** Find out - it usually is not.


don't think either of them winds audio trannies anyway


** All toroidals are audio quality.


I was once told by one company that they buy in torroids with pre-wound
primaries and just wind secondaries onto them. We don't use that company
now!


** Why ever not ??? - that is a most efficient way to do business .

You are one pompous little pommy prick aren't you .





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

"Yves Monmagnon"


A 6L6 PP calls for a 6K load where 115 Vac corresponds to 2.2 Watts. Core
being already stressed.


** There are ***two*** 115 volt primaries - so better make that 8.8
watts.

For AB1 with 360 volt plate supply the optimum load is 3800 ohms - so
better make that 14 watts now.

If triode connected the load Z and V swing is less again - might work
out OK.

See how easy it is to select the facts to suit the conclusion you want ???





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

On Sat, 17 Jan 2004 11:09:54 +1100, Phil Allison wrote:


"Form@C"


I suppose that any dc imbalance could be corrected by using
a low value resistor in series with one winding to even them up.


** How stupid.

The DC imbalance is in the tubes - not the tranny.


No, just mistaken. I had assumed that we were talking about winding
resistance or impedance imbalance here, due to winding the two primaries
as separate windings rather than bifilar.


** Quote:

"The only drawback is the need for *exact * DC current balance in the
primaries."

How can you possibly misread THAT !!!!!!



My idea was to make up any
differences in load - not the valves (which I assumed would be close to
balanced).


** Then you do not know much about valves.



Unfortunately, no doubt due to a genetic deficiency, I was born without
inbuilt technical knowlege of valves and transformers! :-) I'm having to
learn it rather later in life than some...


snip

Many p-p OPTs are ungapped so suffer from exactly the same problem.


** Only toroids have "NO AIR GAP ".

Only toroids saturate with "a few mA of DC imbalance"

All E-core trannies ***have gaps*** - between each E and I
lamination.


So the "softer" core material of the torroids causes it to saturate more
easily. It doesn't compensate for the lack of gap (as I originally
thought it might), and actually increases the necessity for gapping?


Their cores are also carrying dc but don't saturate as the net flux is
zero - or close to it. I
realise that balance would be more critical in this instance because
the transformer is running much closer to saturation than a "proper"
OPT.


** You are wrong again.

If the primary is wound with enough turns to avoid core saturation
at 20
Hz then the sensitivity to DC imbalance gets WORSE !!!!



I don't mind being wrong: it's all part of learning.

So a mains transformer, having less primary turns and designed to saturate
at just below 50Hz, would be *more* tolerant of imbalance if wound on iron
then. There is less magnetisation effect for the same primary current. The
"magnetically soft" nature of the torroidal GOSS core makes it more
sensitive to saturation in the first place though, so this makes the
problem worse, to the point where saturation occurs at very low DC
currents.


PP tube amps that use toroidal OTs also usually have servo bias
balancing
systems - or owners prepared to do the same manually on a regular
basis.


I see.... Thanks again, Phil.

--
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... :-)

"Form@C" wrote in message
news
On Sat, 17 Jan 2004 00:58:33 +1100, Patrick Turner wrote:

snip

Suppose you had a P of 240v to 2 x 20v S. The 20v could be paralleled,
so
you'd have a 240:20 turn ratio which is 12 :1 which is a bit low for
most
tube applications unless you use low impedance tubes, like 6AS7G. 12:1
turn ratio is 144:1 Z ratio, which means you'd have 1,152 ohms to 8
ohms,

snip


Around here I can get 115+115v:9+9v 30VA, which I work out to be
5224.7R:8R if I parallel the secondaries, which would be just about ideal
for a pair of 6L6s in p-p. Providing the two primaries are sufficiently
similar, of course. I haven't tested any, but I would assume that they
would be pretty close as the primaries (and secondaries for that matter)
are specified to be parallelled under normal use, and any mismatch would
cause heating. I suppose that any dc imbalance could be corrected by using
a low value resistor in series with one winding to even them up. Using a
p-p output stage gets rid of a lot of the dc problem of course. The 30VA
size should normally pass somewhere around 130mA when used as a
mains tranny, so the wire size (at least) should be happy with the
70-100mA of a 6L6. Once again, this is educated guesswork on my part, the
primary may saturate at a frequency too high to be useful.

For a given core, induction depends on the voltage applied and the
frequency, no matter
the power extracted from the tranny.
Using a 300VA unit to feed a 10VA load DOES NOT AFFECTS INDUCTION !
If a tranny was designed with an induction of say 1.4 Tesla (already hi) at
230 Vac, 50Hz, and want use it at
25 Hz, then the rms voltage applied must be halfed (115 Vac) to maintain the
same induction level.
So, such trannies are useful for low voltage / hi current valves.
Good news ! Those lo Rp's toobs don't call for hi primary inductance.
All that was stated above looking for Z ratio and power handling remains
true of course.

A 6L6 PP calls for a 6K load where 115 Vac corresponds to 2.2 Watts. Core
being already stressed.

(Hey, a Circlotron PP vith 2 triode connected EL34 calls for a1000 Ohms
load, where 115V rms will produce
near 13 Watts. A 9V secondary will match an 8 Ohm speaker.)

Yves.


--
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... :-)

"Form@C" wrote in message
news
On Sat, 17 Jan 2004 11:09:54 +1100, Phil Allison wrote:


** Only toroids have "NO AIR GAP ".

Only toroids saturate with "a few mA of DC imbalance"

All E-core trannies ***have gaps*** - between each E and I
lamination.


So the "softer" core material of the torroids causes it to saturate more
easily.


** Are you insane ??

Where ever did "softer" come from ?????


It doesn't compensate for the lack of gap (as I originally
thought it might), and actually increases the necessity for gapping?


** Huh ? A continuous spiral of GOSS has NO ****ING GAPS !!!!

Good quality E-cores and all C cores use GOSS.

The material is not the issue.




** You are wrong again.

If the primary is wound with enough turns to avoid core saturation
at 20 Hz then the sensitivity to DC imbalance gets WORSE !!!!



I don't mind being wrong: it's all part of learning.


** Making dopey presumptions that contradict facts already posted is NOT
part of learning.



So a mains transformer, having less primary turns and designed to saturate
at just below 50Hz, would be *more* tolerant of imbalance if wound on iron
then.


** What drugs are you on - or not on ????

The material is not the issue - air gaps and number of turns is.

The more turns the more induction and the nearer you get to saturation for
a given imbalance current.



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

"Yves Monmagnon"
"Phil Allison"
"Yves Monmagnon"


A 6L6 PP calls for a 6K load where 115 Vac corresponds to 2.2 Watts.
Core being already stressed.


** There are ***two*** 115 volt primaries - so better make that
8.8
watts.

But I halved the voltage to halve the induction.


** A few points to ponder:

1. The core of a mains toriod is not "stressed" at nominal voltage and
frequency.

2. The inductance is extremely high ( due to having no air gaps) so
magnetising current is very small - a few mA for a 100 VA, 240 V tranny.
Core saturation effects start at about 10% above nominal voltage ( or below
nominal frequency) and are sudden and hard.

3. If used for tube output matching then the benefits include low harmonic
distortion at LF - from the low Imag, wide bandwidth and low cost.

4. One would not use a nominal 30 VA toroid for a 30 watt output amp -
the copper losses would be 12 - 15 % of the input power, a larger core is
needed to offset that - say a 50 or 80 VA one. This makes fitting the
necessary turns easy.

5. If a pair of tubes ( classA 6L6s ? ) could deliver 30 watts, using a
given toroidal tranny, in the mid band and maintained this figure down to 45
Hz, then it could still deliver 15 watts at 30 Hz - ie the -3dB power
bandwidth extends down to 30 Hz.

There is no sensible reason to say that such an amp is not of good quality
when driving hi-fi speakers that (like most) also roll of below 45 Hz and
have much reduced power handling down there too.





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

"Phil Allison" wrote in message
u...

"Yves Monmagnon"


A 6L6 PP calls for a 6K load where 115 Vac corresponds to 2.2 Watts.
Core
being already stressed.


** There are ***two*** 115 volt primaries - so better make that 8.8
watts.

But I halved the voltage to halve the induction.


For AB1 with 360 volt plate supply the optimum load is 3800 ohms - so
better make that 14 watts now.

If triode connected the load Z and V swing is less again - might
work
out OK.

See how easy it is to select the facts to suit the conclusion you want
???

Yeap !
It's why chats are made for ! (arn't ?)

Yves.





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

On Sat, 17 Jan 2004 20:48:28 +1100, Phil Allison wrote:

snip

I was once told by one company that they buy in torroids with pre-wound
primaries and just wind secondaries onto them. We don't use that company
now!


** Why ever not ??? - that is a most efficient way to do business .

You are one pompous little pommy prick aren't you .



We don't use them because they don't exist now, in spite of it being a
sensible way of working. I didn't give a reason in my previous post... :-)


--
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, 17 Jan 2004 20:44:18 +1100, Phil Allison wrote:


"Form@C"

Phil Allison wrote:


** Error #1 - any split primary ( 2 x 120 volt) tranny is made
for
50 Hz operation.


Is it? That's interesting. I would have thought that 110+110 or 120+120
would have been intended for the american market and 60Hz,


** How so - there are no 240 volt GPOs in the USA.


I thought it used to be 110-earth for single phase lighting/small power
and 220v line-line power circuits, with 120 (nominal - 127 really) to
earth from the phases. This may be very old info now and may well have
changed.


wheras a 115+115 would have been european and 50Hz.


** Spit primaries are for dual voltage operation - means USA or
Europe.

USA power is nominally 117 volts 60Hz. 115 and 120 are just
approximations.


Handy to know...





** Error #5 - the tranny just needs to be a twin 240 type.

As I pointed out to Patrick though, that means a custom winding and it
may not be economically feasible.


** Those who do not know need to find out.

NOT MAKE ****ING STUPID ASSUMPTIONS !!!!!!!!!!!!


Even something like 240/110+110 isolating
tranny is almost certain to be a special order on an oversized core
.....


** Rot. Toroidal makers have numerpous cores in stock with
primaries
already wound - just waiting for customers to order the secondary
windings they need. There is no need to adjust the core size for
different voltages since the primary always occupies under half the
available space.


Thanks, but you appear to be in the happy position of having some decent
winders there! As I said before, I'll ask around. I may very well get some
wound without it costing a packet. I'll let you know how I get on. I *do*
know for certain that we pay quite a bit (over 50%) more for custom EI
transformers than for standard "list" items of similar VA rating.

--
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... :-)

Your third grade responses are unneded and unwanted.
My wife is a practicing PSYCHOLOGIST and she said
that you need help.




On Sat, 17 Jan 2004 01:12:46 +1100, "Phil Allison"
wrote:


"Patrick Turner"


The response for a mains toroidal is surprisingly wide,
anything from a few Hz to maybe 100 kHz.


** That's what I said already - you asshole.



Suppose you had a P of 240v to 2 x 20v S.
The 20v could be paralleled, so you'd have a 240:20 turn ratio
which is 12 :1 which is a bit low for most tube applications unless
you use low impedance tubes, like 6AS7G.
12:1 turn ratio is 144:1 Z ratio, which means you'd have 1,152 ohms to 8
ohms,



** Suppose the Turneroid was not an asshole - then he might not post so
much stinking ****e.



which means that to get a match, you'd need say 4 x EL34 all paralleled
for a class A SE amp.
To keep the DC out of the tranny because you have no CT, you coulod have a
large choke to supply DC to the tubes,
and cap couple the OPT, and you would get about 35 w into 1152 ohms, which
is
200vrms on the primary, and unfortunately, the core would saturate at about
35 Hz, because at the normal 240v across the primary,
the B would be about 1.2T at 50 Hz, and we really want about 3 times the
primary turns to give
an ideal bass response.


** Suppose the earth was flat - the the Turneroid would be an expert on
curved surfaces.



Using the mains tranny in a circlotron design with 4 x EL34 is also
possible,
as the DC flow is about the same in both directions across the P winding,
and thus there is no need for a choke feed.


** Suppose the Turneroid were to choke - then there is no more need to
feed him too.



Inbalance and poor bass capability are still present.
To do any better, the tubes should be say 4 x 6AS7G, which
could make about 25 watts class AB, perhaps with a lower turn ratio.

Not many mains toroidals have two identical 240v windings,
and a set of secondaries.


** The Turneroid is such an utter ****WIT !!!

Custom toriods are available from any winder at low cost !!!!!



BUT, if you could find a toroidal 1:1 240v isolation tranny,


** If you could find the tooth fairy ..........



it may be possible to wind on some secondaries over the primaries,
but this still isn't ideal because there are still not enough turns to allow
low bass at full power with KT88,EL34,6L6 type of tubes,
and the two P halves of the winding have asymetric leakage inductance
to the wound on low voltage winding.

So, to cut a long story short,


** Simply shoot the Turneroid.

Amen.




.......... Phil

As I pointed out to Patrick though, that means a custom winding and it may
not be economically feasible.

** Those who do not know need to find out.

NOT MAKE ****ING STUPID ASSUMPTIONS !!!!!!!!!!!!

Even something like 240/110+110 isolating
tranny is almost certain to be a special order on an oversized core .....

** Rot. Toroidal makers have numerpous cores in stock with primaries
already wound - just waiting for customers to order the secondary windings
they need. There is no need to adjust the core size for different voltages
since the primary always occupies under half the available space.

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

Phil, you are leading everyone astray by suggesting ppl try purchasing
toroidals for OPT use in PP tube amps when there are simply not enough
primary turns on the core, and even if the primary turns were
doubled at a buyer's request, this still does not reduce the operating B
to get saturation at full power to below 20 Hz.

The arrangement of windings for a PP tube amp requires very careful
winding and the P&S layers well interleaved , and if you think the average
Richard Cranium winder could ever get near Plitron OPT standards by starting off
with a toroid which already has a
mains winding on it, then you also must be Richard's dull brother.

It does not matter if you had a huge core suited to 1 kW mains use,
the same thing applies, because as the core size increases, the turns per volt
reduces, so keeping B about the same and there is no advantage
in using a huge toroidal to try to get good bass, unless the turns are
dramatically increased.

OPTs should be wound to take into account
saturation, winding losses, inductance, HF response, leakage inductance,
and stray capacitance.
Because tubes are high output impedance devices, even when used in triode,
particular attention must be given to all parameters,
so before anyone could recommend mains trannies for tubed hi-fi amps,
they need to be very careful with the turns per volt for any given
transformer.
A mains tranny is usually set up to run at 1.2 Tesla at the rated voltage for
any winding,
at say 50 Hz, but for hi-fi, we want 1.2 Tesla at 12.5 Hz, and to get that we
need 4 times the turns per volt, and 6 times the turns per volt is not overkill.

And this don't take into consideration that a PP tube amp's primary anode to
anode voltage
might be 500 vrms, over twice the 240v.
So instead of 1 x 240 volt winding, we should have 4 x 240 v winding, or
better, 7 x 240v windings.

A typical toroidal mains tranny with a cross sectional iron area of say
50mm x 50mm might have a primary of 360 turns, which is 1.5 turns per volt,
and the wire would be thick to take the high current input..

But a decent audio OPT would have at least 2,000 turns on the same
cross section of core, with much thinner wire, since tubes operate with
****ant currents, but a large voltage swing.
P&S windings should be carefully set out so that total winding losses are less
than
5%, and losses should be equal in each of the P&S windings.

Williamson used 4,400 turns on his OPT with a core leg
of 32mm x 44mm, and yet the bw was excellent, and the losses
were only 10% and saturation at such a LF that one can neglect it.
But his amp design was for PP KT66 in triode, for a lousy
16 watts into a plate to plate load of 10k, where Va-a is 400v.
UL versions of the same amp would have Va-a = 547v.
It is practical to double the core leg area, and halve the turn numbers,
thus reducing the P inductance but still have sufficient Lp,
yet still we need 2,000 P turns to keep the B at the same good
value as Williamson achieved in 1947.
The lower Np reduces leakage inductance, for a given wind up geometry.

The tranny winders I know and who I have tried to deal with
don't have much of a clue about how to wind a wide band
OPT for tubes, they can only rely
on what the buyer or an engineer tells them.
Most throw up when I tell them what is really required for a decent OPT,
so I just wind my own.

Patrick Turner.

On Sat, 17 Jan 2004 21:20:46 +1100, Phil Allison wrote:


"Form@C" wrote in message
news
On Sat, 17 Jan 2004 11:09:54 +1100, Phil Allison wrote:


** Only toroids have "NO AIR GAP ".

Only toroids saturate with "a few mA of DC imbalance"

All E-core trannies ***have gaps*** - between each E and I
lamination.


So the "softer" core material of the torroids causes it to saturate more
easily.


** Are you insane ??

Where ever did "softer" come from ?????


It doesn't compensate for the lack of gap (as I originally
thought it might), and actually increases the necessity for gapping?


** Huh ? A continuous spiral of GOSS has NO ****ING GAPS !!!!

Good quality E-cores and all C cores use GOSS.

The material is not the issue.




** You are wrong again.

If the primary is wound with enough turns to avoid core saturation
at 20 Hz then the sensitivity to DC imbalance gets WORSE !!!!



I don't mind being wrong: it's all part of learning.


** Making dopey presumptions that contradict facts already posted is
NOT
part of learning.


I am *not* making presumptions - that is why I am having this discussion.
I am genuinely trying to understand. Unfortunately, transformer theory
isn't something that I have grown up with. The workings of audio
transformers in particular are relatively new to me.


So a mains transformer, having less primary turns and designed to
saturate at just below 50Hz, would be *more* tolerant of imbalance if
wound on iron then.


** What drugs are you on - or not on ????

The material is not the issue - air gaps and number of turns is.

The more turns the more induction and the nearer you get to saturation
for
a given imbalance current.



mmm... I obviously phrased that very badly. In response to:
" If the primary is wound with enough turns to avoid core
saturation
at 20 Hz then the sensitivity to DC imbalance gets WORSE !!!!"
I was trying to say that, as mains transformers have far fewer primary
turns than audio transformers (and are designed to saturate at a
frequency 20Hz), then for a given dc current isn't there less magnetising
effect in the core? Shouldn't that make them more tolerant of unbalanced
dc when used as p-p output tranny? I had failed to pick up on the fact
that, although an EI core could possibly be more tolerant, a torroid won't
be simply because it is completely gapless and can't really stand *any* dc
magnetising current without saturating. This is made even worse because
the transformer has been designed to operate close to saturation anyway
(to keep the core size down, I assume.). Sorry.


Sheesh, Phil! I'm having to read through your (almost) abusive messages to
get to the good bits! You are giving me what appears to be very good info
though. If you weren't you would be in my killfile by now. ;-) Thanks
anyway. I know this all seems so simple to you and I must appear really
dumb to not be able to see it...

--
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... :-)

"Form@C" said:

Thanks, but you appear to be in the happy position of having some decent
winders there! As I said before, I'll ask around. I may very well get some
wound without it costing a packet. I'll let you know how I get on. I *do*
know for certain that we pay quite a bit (over 50%) more for custom EI
transformers than for standard "list" items of similar VA rating.

Dunno about the situation in the UK, but here on the other side of the
Channel we're blessed with some custom winders who can supply us tube
(valve) heads with almost anything, be it EI or toroidal.
Custom windings usually are +20 % over stock types.

--
Sander deWaal
Vacuum Audio Consultancy

"Form@C" wrote in message
news
Sheesh, Phil! I'm having to read through your (almost) abusive messages to
get to the good bits! You are giving me what appears to be very good info
though. If you weren't you would be in my killfile by now. ;-)

Psst... he's in 90% of ours already.. has been for three months...
Frankly I'm suprised you've held on as long as you have!

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

On Sat, 17 Jan 2004 13:21:36 -0600, Tim Williams wrote:

"Form@C" wrote in message
news
Sheesh, Phil! I'm having to read through your (almost) abusive messages
to get to the good bits! You are giving me what appears to be very good
info though. If you weren't you would be in my killfile by now. ;-)

Psst... he's in 90% of ours already.. has been for three months... Frankly
I'm suprised you've held on as long as you have!


I'll put up with people reasonably well - providing they don't go too far.
Phil has, quite rightly, been pointing out my errors - albeit in a rather
"forthright" way. ;-) So far he hasn't upset me much and has certainly
helped me. I should really have gone looking for transformer info myself,
but most of the stuff on the net seems to be rather advanced. Sometimes I
suppose I need the point "hammering" in a bit! If all he has achieved is
to make me look elsewhere, it's something. :-)

--
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... :-)

"Form@C" wrote in message
news
Sometimes I suppose I need the point "hammering" in a bit!

Reminds me of a quote from Choky:

Masochist: "Hurt me!"
Sadist: "No!"
)))

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

On Sat, 17 Jan 2004 20:44:18 +1100, "Phil Allison" wrote:


"Form@C"

Phil Allison wrote:


** Error #1 - any split primary ( 2 x 120 volt) tranny is made
for
50 Hz operation.


really?? shame I have a bunch here at 60hz...


Is it? That's interesting. I would have thought that 110+110 or 120+120
would have been intended for the american market and 60Hz,


** How so - there are no 240 volt GPOs in the USA.


really? I have a 240 volt outlet in my dining room for my air conditioner... my American air conditioner...