Hi all,

I'm thinking of building a tube bass guitar amp (frequency response 40-10kHz
needed) using a toroidal output transformer.

Someone suggested using toroidals to me so as to keep the weight down (or
more likely, to squeeze more power out of the same weight) and also said
that a standard mains transformer would be fine. I've looked everywhere I
can think of for information on GOS toroidal core mains transformer
frequency responses but can't find that kind of information anywhere -
except plitron. They list the upper limits of GOS as being 2kHz which sounds
quite wrong to me.

Can anyone point me in a good direction to find this info?

Thanks.
cb

"Chris Berry"


They list the upper limits of GOS as being 2kHz which sounds
quite wrong to me.


** They ****ing well do not - you are an IDIOT !!!!!




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

"Phil Allison" wrote in message
u...

"Chris Berry"


They list the upper limits of GOS as being 2kHz which sounds
quite wrong to me.


** They ****ing well do not - you are an IDIOT !!!!!

Oh you again...
Who won the Rugby world cup?
cb

Chris Berry wrote:

Hi all,

I'm thinking of building a tube bass guitar amp (frequency response 40-10kHz
needed) using a toroidal output transformer.

Someone suggested using toroidals to me so as to keep the weight down (or
more likely, to squeeze more power out of the same weight) and also said
that a standard mains transformer would be fine. I've looked everywhere I
can think of for information on GOS toroidal core mains transformer
frequency responses but can't find that kind of information anywhere -
except plitron. They list the upper limits of GOS as being 2kHz which sounds
quite wrong to me.

Can anyone point me in a good direction to find this info?

Thanks.
cb

There is a major problem about trying to use toroidal mains trannies for
PP audio amps.

If you live in a 110v mains area, which is the US, then there are nowhere
near enough turns on a 500VA transformer primary so that
50 watts of bass power could be had.
There probably isn't even a centre tap!

If you are doing a bass amp for 50 watts into say 5k anode to anode,
then if the core cross sectional area is 50mm x 50mm, ( 2" x 2" ), which is
large, then
about 1,000 primary turns are required so saturation does not occur.
50 watts is 500 vrms into the load, and with 2,000 turns around 50 x50,
the field strength of 1.5 Tesla will be at 30 Hz.

Most mains trannies run so 1.5 Tesla exists at 110v at 60 Hz.
So the turns required for 50 x 50 will be only 165 turns.

So with such a mains tranny, saturation at 1.5 tesla will occur at 182 Hz,
which is a lousy result for a bass amp.

The frequency response of toroidal opts, even mains types
is usually good enough to get to maybe 100 kHz easily.
But that's because the turn number are low, so leakage L is low,
and LL rises in proportion to the square on the turns,
so for ten times the turns, the LL is 100 times as great for the same
geometry of windings.

With E&I mains trannies, the leakage inductance between P&S windings is around
100 mH+ referred to the primary, hence the 2 kHz bandwidth.
Toroidals are better, because the proximity of P&S
has both windings close to each other for a traverse width which goes
all the way around the circle of the toriod, and its equivalent
to some 3 x 2 interleaving pattern on an E&I tranny.


So, to sum up, there is no way you can use a mains tranny for
a bass amp, even though you won't need bandwidth above 2 kHz.

Plitron make some nice audio trannies, and I suggest you buy one.
Perhaps a Hammond may suit you quite well, and it'll be cheaper, afaik.

Even buying a mains tranny with 2 x 120v primaries for countries where
50 Hz x 240v exists won't improve the situation much.

All transformers are subject to magnetic saturation even without a load,
and the phenomena is dependant on applied voltage and frequency.
The LF saturation only varies slightly between all the main steels used,
so low grade non oriented silicon steel, NOSS, saturates
at only 10% lower F than NOSS.
Either steel is useful for audio trannies.
The U of the iron reduces as F rises, and a good OPT
can have its cores removed and the windup still works OK at 10 kHz,
because an air cored winding will have enough inductance at 10 kHz.
In fact, the presnce of poor iron causes iron losses at HF, but at least with
fine thin lams of GOSS in either E&I or toroidal cores the HF losses are lower.
The LF distortion is also a lot lower in GOSS steel, so don't be afraid of it,
its great stuff, wherever you find it.

The reason you cannot find any info on the F response of a mains tranny
is that nobody uses any for audio, and most certainly not for tube audio.
The ratios avaialable are also all wrong for a 5k to 8 ohm
load.

99% of mains trannies are designed to run as close as possible to magnetic
saturation, ie, about 1.2 Tesla, and with poor iron, the
irn heats up, and with GOSS, it heats up minimally, but
it gets noiser as the operating B goes higher.

The best mains trannies are designed to run at 0.8 Tesla or less,
and with thick enough copper to
reduce the winding and copper losses, so that temp rise after 4 hrs is less
than 10 degrees.
But this means a core 3 times the weight of the lowest common denominator
rubbish
from bean counter designed commercial trannies, which often are noisy, and run
hot.

With OPTs, the best have at least 2,000 turns around a 50 x 50 core section.
This allows 1.5 Tesla at 15 Hz at 50 watts into 5k.

There is more info on the theory and practice of winding E&I OPTs
at my website, http://www.turneraudio.com.au

I have nothing on Toroidal designs, because to wind one requires
a special machine, and arranging the taps and many winding sections
is a PITA with a toroidal, plus the core is very prone to
DC offset currents due to imbalance in the DC flow in each half of the PP
primary.
Then there is mounting and varnishing, and its all too much bother,
and an E&I or c-cored OPT is easier, and quite effective.

Patrick Turner.

"Patrick Turner" = incorrigible menace to usenet users

Chris Berry wrote:


Can anyone point me in a good direction to find this info?


There is a major problem about trying to use toroidal mains trannies for
PP audio amps.


** No-one ever suggested that the OP use a mains transformer for a tube
bass amp.

The suggestion was that a toroidal tranny wound for the job could be used
to save weight.



If you live in a 110v mains area,


** The OP lives in Europe.


( snip all Turneroid's irrelevant stuff relating to using a mains tranny)



The frequency response of toroidal opts, even mains types
is usually good enough to get to maybe 100 kHz easily.


** This is the only info the OP wanted confirmed.

Hooray !!!!!!!!!!!!!!




So, to sum up, there is no way you can use a mains tranny for
a bass amp, even though you won't need bandwidth above 2 kHz.


** A custom wound toroidal suited to the job of an OT is no problem to get
made.


( snip loads of the Turneroid's boring, self opinionated crap)


I have nothing on Toroidal designs,


** Since RDH4 does not describe them the Turneroid ****head is lost for
info.



because to wind one requires
a special machine,


** So you use someone who ****ing owns one - moron.



and arranging the taps and many winding sections
is a PITA with a toroidal,


** Says a congenital liar who has never seen one being made.


plus the core is very prone to
DC offset currents due to imbalance in the DC flow in each half of the PP
primary.


** So you trim the bias from time to time - no problem for a home brew
amp.


Then there is mounting and varnishing,


** Hey ****head - toroidals use polyester wrap, have done for decades.


and its all too much bother,


** For an 80 year old autistic moron - yes.


OTOH professional transformer winders have no problem - likely knock one
out for you in 30 minutes.





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

It is obvious from the post below that Phil Allison
has nothing worthwhile to offer the group
or to the original poster, so we could wish Allison to please **** off,
he ain't wanted here now, and he ain't ever been wanted here.
The newbies here ought to realise that Phil Allison is the most
hate ridden and foul mouthed poster here on the Internet,
and replying in any detail to him will often bring a tirade of
insults, utterly undeserving. Please do not respond to his posts,
unless you enjoy being butchered.
He is like the teacher who beats up his students for their ignorance.
He believes the Net is only for those who know it all like him,
which of course is untrue, since he is a poseur elitist.
Please notice how he cut my post to ribbons during his reply to me,
and fails to engage in any meaningful response.

In case anyone was led astray by Allison's BS on toroidals,
then please consider the following points.

I don't believe the real situation with custom winders and DIY hobbyists
is that much different in europe or the US etc, compared to what it is here in
Oz.

I have tried in vain to get any commercial winder like Harbuch at Hornsby
in Sydney, or Tortech to be able to produce a decent
toroidal tranny suited specifically for a tube bass amp
in a time frame of 30 minutes as you suggest, and at a competive price
compared to Plitron who makes special audio toroidals of good quality, or
Hammond who makes
E&I lam types, some of which are ideal for bass amp use.
Any non standard transformer wound to my exacting specs from these
winders would cost lots more than any standard item of the same weight and
turns/labour.
Both the above companies have quoted me absurd prices for what I wanted,
and Harbuch plain refused to quote when I stipulated the turns/volt ratio
I wanted for a mains tranny.
Harbuch once offered two outputs and a mains tranny, and a choke for aud $ 1,200

back in 1995, as a kit of the four iron wound items, to suit a pair of 25 watt
UL channels.
Tortech quoted me aud $1,600 for the same thing in 1995, and they said they
couldn't do
a fine wired audio toroid, and that they'd have to import them from a company in
NZ,
which now appears to have dissappeared.
Other companies were as expensive, or would take forever to do the order,
so I gave up and have wound all my own trannies for my amps ever since.
I shudder to think what these companies would quote me now, or what
quality they would try to dump on me.
I believe it is false economy to ask such supposedly specialist winders to
ever wind anything for me, and if I wanted to use toroidal OPTs, i'd save up
and go to Plitron.
The material costs are less than 10% of the above prices mentioned for the iron
wound components.
A 5 Kg tranny has material costs of aud $9 per Kg, so $45 total, which is what I
would have to pay,
but these companies buy cheaper by the tonne, not by the Kg, like I have to.
So for 30 Kgs of trannies, enough iron for a stereo 50-50, I pay $270 for
material,
and I don't spend a cent on unhelpful "specialists."

There is no way that stock standard mains trannies from Dick Smith Electronics,
Altronics, or Jaycar, ( all companies like the us's Radio Shack ) constitute
great quality even for mains use.
AFAIK, these are all sourced from some cheapo asian factory.
All the ones I have tried to use have been too noisy for hi-fi.
It would be impossible to use any of their stocks of mains trannies for a PP
tube bass amp.

The original poster was implying his intention was to
buy a ready stock standard mains tranny for bass in a tube amp.

The only possible way a mains tranny could be used for a bass amp
would be with transistors or mosfets transformer coupled.
We have argued all this before at aus.hi-fi, and I assume its all in the
archives what was said.
But our questioner here is wanting to use tubes, not solid state.
The lower voltages used with SS does allow toroidal mains trannies to be used as
audio output trannies.
The mains primary is not used in this case.

Nearly all the commercial mains toroidals I have tried to use have been
too noisy to use for hi-fi amps, because the tape wound
insulation allows some tiny amount of vibration between layers of windings,
especially with rectifiers connected,
and unless they are thoroughly vacuum impregnated with varnish and baked,
and preferably potted, they are all but useless engineering to me.

Allison's post fails dismally to take into account many of the technical issues
raised in mine,
such as core saturation and turn numbers and it seems you lack much knowledge on
transformers.

My advice to Allison is that he please ****s off to where he belongs, in a sewer
with all the other
slime, ooze, and cockroaches, and he shouldn't come out unless he can restrain
himself
from needlessly filling pages with insult which prooves his dullness,
lack of concern for others, and general dipleasure and disrespect for all those
around him.
Until he shows respect, and behaves with courtesy at all times,
and recommences his medication program,

Then he should stay away from here.

Patrick Turner.




Phil Allison wrote:

"Patrick Turner" = incorrigible menace to usenet users

Chris Berry wrote:


Can anyone point me in a good direction to find this info?


There is a major problem about trying to use toroidal mains trannies for
PP audio amps.

** No-one ever suggested that the OP use a mains transformer for a tube
bass amp.

The suggestion was that a toroidal tranny wound for the job could be used
to save weight.

If you live in a 110v mains area,

** The OP lives in Europe.

( snip all Turneroid's irrelevant stuff relating to using a mains tranny)


The frequency response of toroidal opts, even mains types
is usually good enough to get to maybe 100 kHz easily.

** This is the only info the OP wanted confirmed.

Hooray !!!!!!!!!!!!!!


So, to sum up, there is no way you can use a mains tranny for
a bass amp, even though you won't need bandwidth above 2 kHz.

** A custom wound toroidal suited to the job of an OT is no problem to get
made.

( snip loads of the Turneroid's boring, self opinionated crap)


I have nothing on Toroidal designs,

** Since RDH4 does not describe them the Turneroid ****head is lost for
info.

because to wind one requires
a special machine,

** So you use someone who ****ing owns one - moron.

and arranging the taps and many winding sections
is a PITA with a toroidal,

** Says a congenital liar who has never seen one being made.

plus the core is very prone to
DC offset currents due to imbalance in the DC flow in each half of the PP
primary.

** So you trim the bias from time to time - no problem for a home brew
amp.

Then there is mounting and varnishing,

** Hey ****head - toroidals use polyester wrap, have done for decades.

and its all too much bother,

** For an 80 year old autistic moron - yes.

OTOH professional transformer winders have no problem - likely knock one
out for you in 30 minutes.

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

Phil Allison wrote:
"Patrick Turner" = incorrigible menace to usenet users


Chris Berry wrote:


Can anyone point me in a good direction to find this info?


There is a major problem about trying to use toroidal mains trannies for
PP audio amps.



** No-one ever suggested that the OP use a mains transformer for a tube
bass amp.

Which bit of "and also said that a standard mains transformer would
be fine" (from the OP) were you unable to read?
Doh.

Andy

On Tue, 06 Apr 2004 11:13:14 +0200, Chris Berry wrote:

Hi all,

I'm thinking of building a tube bass guitar amp (frequency response
40-10kHz needed) using a toroidal output transformer.

Someone suggested using toroidals to me so as to keep the weight down (or
more likely, to squeeze more power out of the same weight) and also said
that a standard mains transformer would be fine. I've looked everywhere I
can think of for information on GOS toroidal core mains transformer
frequency responses but can't find that kind of information anywhere -
except plitron. They list the upper limits of GOS as being 2kHz which
sounds quite wrong to me.

Can anyone point me in a good direction to find this info?



grins
Now, this is where I came in, isn't it Phil and Patrick? Thanks lads... :-)

Chris,
You won't find any info because there isn't any.
If you want to experiment then try this:
Get a toroidal winder to produce you a core of about 60VA with two 240v
windings - or, if possible, two identical windings with as many turns as
they can fit - probably about 2000 turns each. It is limited by the
minimum size of wire that they like to put through the winder. Hand wind
your own secondary, calculating it to suit your required ratio. Now comes
the hard bit. You need a p-p output stage with balanced current in each
half of the winding (both big windings in series to produce a tapped
primary, of course). This will almost certainly need a servo amp to
control the grid volts of one valve from the cathode voltage, compared to
the cathode voltage of the other. As Phil pointed out to me in no
uncertain terms, you can't accept *any* out of balance DC in the primary
of a toroid as it saturates with very little current because there is no
air gap.

I had fun trying to find someone who would produce the toroid that I
wanted. I was getting stupid quotes, so shop around. Try some of the
smaller companies and make it clear that it is essentially a 1:1 240v
isolating transformer that you want. They can understand that, but not
audio!

I just happen to have a toroid with the primaries suitably wound and
waiting for a chance to do some experiments myself... :-)

--
Cheers...
Mick
Gave up on viruses & trojans - moved to Linux... :-)
Nascom & Gemini info at http://www.nascom.info

"Patrick Turner" wrote in message
...
snip
Thanks for the informative post Patrick - There's a lot of information there
and it will take time to digest....

To add a bit of background, I'm intending on using a fair few more watts
than 55!

My initial theorem, which is useful insofar as if it is theoretically
possible, then there's a very good chance that I might act on it, asks the
question "how light is it possible to design a kt88 based amp with at least
200W of power (300W or 400W would be better for me though) for bass"

To give you an idea as to why I need so much power, I'm currently using a
2400W RMS solid state amp to power my bass rig so it should be able to
handle my speakers with ease...

Anyway, back to your comments... I found your website most helpful and am
still wading through your comments.
Plitron, afaik make transformers that are a little on the pricey side and
way overengineered (at least 25% over) for my purposes.

There are companies round here that wind to spec and for very reasonable
prices. - If I can wade through the theory...

To put it simply, without a toroidal OPT, I can't get close to my weight
aims and $500 for a Plitron transformer just isn't on the cards... maybe
getting a custom one from Plitron - but then again I'm in the same
ballgame...
http://www.plitron.com/PDF/PB/specs/pat4140-00.pdf
Is more than 50% overengineered for my purposes for instance and has a
canadial list price of $444 - add on import duties...

If you know of web resources that can help me calculate the design
parameters for a toroidal OPT precicesly enough, I can get a 700VA made up
locally for under $100 - surely that core is enough for an OPT?

Thanks once more for the time and effort taken in supplying me with all the
info.
cb

"Patrick Turner" wrote in message
...
In case anyone was led astray by Allison's BS on toroidals,
then please consider the following points.

I don't believe the real situation with custom winders and DIY hobbyists
is that much different in europe or the US etc, compared to what it is
here in
Oz.

I don't know but I could check. I know of 2 companies in Europe that will
custom wind *any* (according to them) toroidal and one in the US specialised
in audio trannies that also wind toroids.

snip - anecdotal and interesting followup

Thanks for that...
cb

"Andy Cowley" wrote in message
...

Which bit of "and also said that a standard mains transformer would
be fine" (from the OP) were you unable to read?
Doh.

Andy, let's see if you can recognise the style cof this response copied and
pasted from another NG - on the same subject:

** There is no difference for an OT.

A standard mains toroidal design will do fine for a your purpose.

How's spring in Bath these days? It's been a long time (20 years) since I
last passed by!
cb

"Phil Allison" wrote in message . ..

** For an 80 year old autistic moron - yes.

Why Phil, I had no idea you were 80 years old! Autistic, yeah, moron, sure, but 80 years old? Who'd have thought an 80
year old could be such a complete jerk?

Phread

Chris, if you're planning to use a toroid opt in a big amp, you should read this page, esp. the section on controlling
the bias with servos to keep the dc balanced in the opt.

http://www.normankoren.com/Audio/TENA.html

Phread

Chris Berry wrote:
My initial theorem, which is useful insofar as if it is theoretically
possible, then there's a very good chance that I might act on it, asks the
question "how light is it possible to design a kt88 based amp with at least
200W of power (300W or 400W would be better for me though) for bass"


How about a pair or even quad of 811As running class B? You don't really
need something meant for hifi. A quad should get you a low enough plate
resistance to use cheaper transformer. A pair running class B will give
you 235 watts.


Adam

"Andy Cowley" = utter pommy moron



Which bit of "and also said that a standard mains transformer would
be fine" (from the OP) were you unable to read?


** The OP's claim is wrong.

Duh.




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

"Chris Berry" = dumbest **** on usenet


** There is no difference for an OT.

A standard mains toroidal design will do fine for a your purpose.



** That does not say to use an off the shelf mains tranny.

It clearly stated in the thread that a special wind was needed for OT
use.

This Chris Berry ****wit has pulled words out of context.

Just like he is constantly pulling his tiny cock.





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

"Patrick Turner"

It is obvious from the post below that Phil Allison
has nothing worthwhile to offer the group.....

( snip Turneroid insane diatribe)


** The only obvious thing is that Pat Turner is a criminal.

Criminal threats and vile slander are his game.

The man will spend eternity in hell for that.




......... Phil

Chris Berry wrote:

"Patrick Turner" wrote in message
...
snip
Thanks for the informative post Patrick - There's a lot of information there
and it will take time to digest....

To add a bit of background, I'm intending on using a fair few more watts
than 55!

The wattage isn't of huge concern here to begin with.
The turns per volt are main problem with mains trannies.
Even with two x 240 v primaries wound onto a toroid
you still would get 1.2 Tesla at 480v across the winding at 50 Hz.
it would saturate at 1.5 T at 40 Hz.
Better performance from a well made OPT would give
1.5 Tesla at 480v at 20 Hz, and there would be twice the turns,
ie, the equivalent of 4 x 240v primaries.



My initial theorem, which is useful insofar as if it is theoretically
possible, then there's a very good chance that I might act on it, asks the
question "how light is it possible to design a kt88 based amp with at least
200W of power (300W or 400W would be better for me though) for bass"

I have built 300w+ amps, and the details are at
http://www.turneraudio.com.au/htmlwe.../poweramps.htm

The OPTs weigh near 20 Kgs, or 45 lb.
There is a 100 mm stack of 50 mm tongue material,
and this reduces the primary turns required to only 1,100.
There are 6 sec sections and 5 pri sections for a bandwidth
between 14Hz and 270 kHz, at 300 watts into 1.1k ohms a-a,
working with 12 x EH6550, using cathode bias, and Ea = 480v.

For a bass amp, you need some iron; its not an area where anyone else
ever skimps.



To give you an idea as to why I need so much power, I'm currently using a
2400W RMS solid state amp to power my bass rig so it should be able to
handle my speakers with ease...

So why not stick with SS?



Anyway, back to your comments... I found your website most helpful and am
still wading through your comments.
Plitron, afaik make transformers that are a little on the pricey side and
way overengineered (at least 25% over) for my purposes.

Well I build for the hi-fi market where folks expect power amps to deliver
full power at 20 Hz into the rated load.

This means that for a given number of pri turns, the core must have
twice the weight of a tranny which is only required to get down to 40 Hz.
In my eyes, using the weight isn't overengineering.
But I see your point.


There are companies round here that wind to spec and for very reasonable
prices. - If I can wade through the theory...

I would have your specialist winder choose a 1,000 VA core,
and have him place 2 x 240v primaries on, then all your secondaries,
which I assume you are going to parallel, and then another 2 x 240v secs.

With a 1,000 VA mains tranny, the turns per volt might only be 1 turn per volt,
so its only 240 turns.
960 pri turns would be OK if the core crss sectional area is say 50mm x 44mm.


For the sec, it depends on the load match you intend.
If the load match is 5k to 8 ohms, the Z ratio is 625 : 1
so a turn ratio is the square root of 625, so 25:1.
For 1.25k : 8 ohms, the ZR = 156 :1 so TR is thus only 12.5 :1,
so you'd need 77 secondary turns.
These could be in several paralleled windings,
or one winding around the toroid using quite thick wire,
so that to get low copper losses the sec wire DCR 0.4 ohms,
and also the DCR of the primary 48 ohms.
This will give power losses of less than 10% overall.
But for 5% losses, the wire dia has to be 1.41 times greater.



To put it simply, without a toroidal OPT, I can't get close to my weight
aims and $500 for a Plitron transformer just isn't on the cards... maybe
getting a custom one from Plitron - but then again I'm in the same
ballgame...
http://www.plitron.com/PDF/PB/specs/pat4140-00.pdf
Is more than 50% overengineered for my purposes for instance and has a
canadial list price of $444 - add on import duties...

I didn't say Plitron were cheap.

The cost per watt for a 20 watt OPT is high, but you doing 300 watts,
and then the cost per watt has fallen.

A core rated for mains use of 1,000 VA at least is needed for
an audio tranny wanted for 300 watts bass use.

The cost of winding the 1,000 watt core with more turns suited to
an audio use will only be greater because more copper, insulation,
and labour is used. But the wire used for the primary will be thinner.

One thing for sure, for getting good value, your tranny needs
some professional design work done to get the best.

I wouldn't use a toroidal because of the saturation problem.
The U of the toroid GOSS can be around 40,000 today, due to adavnces in
materials.
The same material used in E&I lams could give about 17,000 in an E&I core.
The E&I use is the equivalent of a very slim air gap.
I now use E&I lams for all my trannies, and its U max is 17,000;
it is the finest material I can get, made in Oz at Newcastle, NSW.
The thd is 1/20 that of NOSS.
In 1955, RDH4 referred GOSS max U at 5,000, E&I lams.
But plain old half priced NOSS is about 3,500 max in E&I lams.
And to my mind, NOSS would be better to use.
The thd generated by NOSS is a much higher than GOSS when away from
voltage levels which cause saturation, but nevertheless its not excessive,
and still a lot less than that produced by the tubes,
and some of my best sounding amps use NOSS cores.
The HF core losses are negligible.




If you know of web resources that can help me calculate the design
parameters for a toroidal OPT precicesly enough, I can get a 700VA made up
locally for under $100 - surely that core is enough for an OPT?

The design above which I mentioned using 960 turns on a 1,000 VA core
should be able to be pushed to give 700 watts at mid frequencies,
but perhaps saturation will occur at 40 Hz or higher F.
The number *MUST* be worked out before winding a single turn.

We need to know exactly what design of amp you are building,
including all the operating and supply voltages.

The winder needs to have a full specification before he starts.


Thanks once more for the time and effort taken in supplying me with all the
info.
cb

The info supplied isn't enough to start spending that $100.

And don't be sore if the cost is $200.

Patrick Turner.

"Yves"


To estimate if a mains tranny is usable as an output one, I suggest the
following rule of thumb:
-Derate voltage by a factor of two.
-Derate power by a factor of four.


** That is a rule of bum - not a rule of thumb.

Toroidals sold for mains use have extremely low magnetising current allowing
full power operation at rated AC voltage at 50 Hz without distortion and
much more at all higher frequencies.



So, do not apply more than 115V ac on a 230V winding.


** Bull****.



To acheive, say 5KOhms load with a standard 2 x 115V winding, the maximum
power will be :


** 230 x 230 / 5000 = 10.5 watts with no saturation at 50 Hz or
above.



Anyway, this doesn't promise anything about hi frequency response.


** Toroids will have their - 3dB point at 50 kHz or above.

E - core mains trannies will only go to 1 kHz or maybe 8 kHz depending if
they are side by side bobbin wound or overwound.



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

Hi Chris.

To estimate if a mains tranny is usable as an output one, I suggest the
following rule of thumb:
-Derate voltage by a factor of two.
-Derate power by a factor of four.

So, do not apply more than 115V ac on a 230V winding.
In turn, for an expected power of 1Kw, this correspond to a load of:
R = U²/P = 115x115/1000= 13 Ohms !!
Even with 2 x 230V winding, at the same power the load won't be higher than
53 Ohms.
Impraticable for tubes !

To acheive, say 5KOhms load with a standard 2 x 115V winding, the maximum
power will be :
P = U²/R = 115x115/5000= 2.6 W and choose a 10 watts unit.
Above, iron starts to saturate.

Anyway, this doesn't promise anything about hi frequency response.

Cheers, Yves.

"Chris Berry" wrote in message
...
Hi all,

I'm thinking of building a tube bass guitar amp (frequency response
40-10kHz
needed) using a toroidal output transformer.

Someone suggested using toroidals to me so as to keep the weight down (or
more likely, to squeeze more power out of the same weight) and also said
that a standard mains transformer would be fine. I've looked everywhere I
can think of for information on GOS toroidal core mains transformer
frequency responses but can't find that kind of information anywhere -
except plitron. They list the upper limits of GOS as being 2kHz which
sounds
quite wrong to me.

Can anyone point me in a good direction to find this info?

Thanks.
cb

Below, Allison insults Yves and tries to lead us all astray.

A 2 x 115v winding on a mains toroidal is usually set up
for 1.2Tesla for the 230v, ie, with 115v across each of two 115v windings in
series.
If the load is 5k, you get 10.6 watts.
BUT, the maximum B is around 1.6 Tesla before severe saturation and distortion
occurs,
and with 230v, that occurs at 37.5 Hz.
If we wanted 50 watts, which would be 500 vrms into 5k,
then the saturation would occur at 81.5 Hz,
and thus the tranny would be quite un-usable for a tubed bass amp,
unless it had about 3 times the turns on the primary, which would have Fs at
27 Hz, and even better if there were 4 times the turns, ie,
8 times the turns needed for 115v, and then Fs would be at around 20 Hz.

So the only bum thinking and bull**** is in Phil Allison's mind.

He tends to go beserko before major festive seasons.
He sure did before last christmas, and he's at it again before easter.

There is some reason behind what Yves has said, although
working the numbers from formulae is more reliable.


Chris Berry originally asked us all about using a mains tranny.
He has since said in a following post that he wanted to make 700 watts,
not just 50 watts.

I have asked him for details of his proposed amp, so we could
design a tranny right here on the group should he wish to do so,
for the benefit of all those here interested in building tube amps.
There are many ways to make 700 watts.
One could use a quad of 813 with a 2,500 volt supply,
for mainly class B operation, ie, low% of class A,
with a high voltage swing, low current swing.

He could have 28 x 6550, with a supply of 500v,
and more conventional v swing and I swing, and have about 350 watts of class A.

Audio Research have made 600 watt amps using 16 x 6550.
That's equal to 75 watts per pair, with a lowish amount of class A.
So on the same basis, one would need 20 x 6550 to make 700 watts.

If the applied signal voltage to the load is the same for 20 tubes as
it is for 70 watts from 2 tubes into 3.6k, ie, 500 vrms, then the load for 700
watts would be about 591 ohms anode to anode.
The turns on the amp with two tubes is the same as required for the
amp with 20 tubes, for the same sized core.
But the 700 watt amp will have to use a core section
about 3 times the area of that of the 70 watt amp, because the dia of the wire
must be so much greater, and thus the winding window needs to be bigger.
For an E&I tranny for 70 watts, a core with a centre leg of
50 x 50 would be adequate, ie, 2,500 sq.mm of centre leg area.
For 700 watts, if we used 3 x 2,500 sq.mm, the core leg would be 86 x 86 sq.mm,
or in real sizes perhaps a 100 mm stack of 75 tongue material.
The P turns could then be 1/3 that of the 70 watt tranny.
The winding window is 38 x 114 mm for this sized core.
A 120 stack of 62.5 tongue would also be OK.

I have used 110 mm stack of 50 mm tongue material for 300 watt trannies,
and to go to 700 watts means the use of the next two tongue sizes
should be evaluated.
I needed 1,060 P turns on my tranny, whose leg is 5,500 sq.mm.
For a core with 7,500 sq.mm, 800 primary turns is all that's required.

The reduction in turns means the leakage inductances are also reduced
proportionately to the square of the turns, so a wind up
with 1/2 the turns and the same overall dimensions has 1/4 the leakage
inductance,
and 1/4 the primary inductance.

If the load is 700 ohms, for 700 watts, as opposed to 3.6k for 70 watts,
then the leakage L needs to be about 5 times lower for 700 watt tranny than for
the 70 watter.
For a 70 watt amp, up to 10 mH of LL would be tolerable,
but with a 700 watter it'd need to be about 2 mH.
Plenty of interleaving easily achieves this on the E&I tranny,
and up to 250 kHz of BW is available, with a 6S x 5P pattern of sections.

A toroidal core with 7,500 sq.mm cross sectional area still needs the same turns

to reach the same result for saturation as any E&I tranny.
A toroid with an area of 7,500 sq.mm would be rated for around
3 Kw for mains use.

It would be with some caution that I would advise anyone trying
to make a toroidal transformer for such high powers,
and high voltages, and I would first suggest that
the question of insulation is crucial with HV,
and perhaps a thouroughly oil filled pot be used for the HV tranny.
If such a tranny fails, its a major problem to wind another.
I think that making sure the oil was able to penetrate the core windings
would be easier with a bobbin wound E&I tranny.
Most certainly the question of saturation due to DC offset is easier to
address for the E&I lam tranny.
The question of weight and mounting a toroidal becomes a problem
as size and weight rises because the weight is on the windings.

With an E&I tranny, the iron suspends the bobbin with its turns, so
there is less static and dynamic pressure on windings.
Neat layer windings on E&I trannies are less prone to pressure caused shorted
turns
of the toroidal, if there are over lapped turns on the same layer.
The use of tape insulation wound over consecutive layers makes the
toroidal wind up somewhat spongy, unless the whole thing is carefully
vacuum impregnated with some special varnish.
The more I think about high power toroidals, the greater the PITA issues.


The use of oil for insulation in addition to plastics has been around for
awhile, but
the techniques of sealing in the oil takes some doing.


Patrick Turner.







Phil Allison wrote:

"Yves"


To estimate if a mains tranny is usable as an output one, I suggest the
following rule of thumb:
-Derate voltage by a factor of two.
-Derate power by a factor of four.

** That is a rule of bum - not a rule of thumb.

Toroidals sold for mains use have extremely low magnetising current allowing
full power operation at rated AC voltage at 50 Hz without distortion and
much more at all higher frequencies.


So, do not apply more than 115V ac on a 230V winding.

** Bull****.


To acheive, say 5KOhms load with a standard 2 x 115V winding, the maximum
power will be :

** 230 x 230 / 5000 = 10.5 watts with no saturation at 50 Hz or
above.


Anyway, this doesn't promise anything about hi frequency response.

** Toroids will have their - 3dB point at 50 kHz or above.

E - core mains trannies will only go to 1 kHz or maybe 8 kHz depending if
they are side by side bobbin wound or overwound.

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

"Patrick Turner" wrote in message
...
Chris Berry originally asked us all about using a mains tranny.
He has since said in a following post that he wanted to make 700 watts,
not just 50 watts.

Well 700W wound be nice....
Down to specifics though, 3 pairs of kt88's would do me fine.
class AB2, 600V on the annodes that would give about 360- 400W no?
That basically concludes what's going in to the OPT but as to what I'd like
out, that would be a bit more complicated wrt ideal impedances.
Ideally, I'd like 2, 2.66, 4 and 8 ohm windings/combinations... so 3 x 4ohm
taps would do fine - 4 would be better so long as they can handle the power.
The reason being that I have both 4 and 8 ohm speaker cabinets and am likely
to use a second 4 ohm cabinet in future. 1.6 ohms would also be nice to
have - but not essential mind you.



I have asked him for details of his proposed amp, so we could
design a tranny right here on the group should he wish to do so,

Sorry, I didn't get around to seeing that offer. I'll take you up on it
gladly.

for the benefit of all those here interested in building tube amps.
There are many ways to make 700 watts.
One could use a quad of 813 with a 2,500 volt supply,
for mainly class B operation, ie, low% of class A,
with a high voltage swing, low current swing.

Patrick, for some things I want to stay within "convention" for guitar amps.
Since weight's a priority, as is a fairly clean sound, I think I'll take the
ab2 kt88 version as being a good compromise and save some weight with the
transformers.
Working out the figures in terms of weight, using toroidal transformers I
should be able to get the transformers for the amp to weigh in at under 9kg
or 20lbs - making a 20kg amp a distinct possibility.
Just to put things into context a Marshall 50W guitar amp weighs 39lbs - I
should be able to build this under 30lbs at a guess.
That's a jump from 1.2W/lbs to 12W/lbs - a signifficant weight advantage.

Some avenues I've taken a quick look at so far include a few unusual
options.
One quite insane one but probably feasible (safety wise there are doubts but
I think the "killer" would be noise) would be to get the HT without a
transformer at all. Just voltage doublerss would give me 500V round here
(220V) but some kind of soft start using relays to wire the thing up so live
and neutral are the right way round.

Another not so insane but probably too good to be true would be to take a
toroidal core and get someone with laser cutting facilities to cut afine
"crack" into the core itself. so long as the "crack was smaller than the
wire diameter, this wouldn't cause problems winding the transformer
(although a solution to that wouldn't be too difficult either).

I have a good partner in crime here - my father - who has considerable
experience with valves albeit mainly on warships and radio - but enough to
stop any major damage. He's 100% original and verging on vintage (gotta love
parents like that) and I've sent a most of the information you've sent my
way for his processing.

Here's one of his deepest darkest responses:

Just an idea (which, incidentally will add a little weight ...)

Since the problem with fixed bias P-P PA stages with Negative feedback is
what happens when they are overdriven - I forget the link you sent me (put
it in here if you pass this on), how about putting a choke in place of the
grid leak. The problem is the rectified grid current not having a discharge
path from the grid, building up an appreciable charge on the grid, pushing
it into grid current operation - to my mind BAD for business - unless you
sell bottles.

The choke will give a low impedance (instead of 100 to 500k resistor) path
to 0V/ground for the DC generated by the grid current as the Amp passes into
overdrive . A cheap choice would be a single ended OP transformer for (say)
2.5 W, with the secondary removed (quite easy since the Secondary is
normally the outside winding). These TFs have an air gap which means that
they can handle the small DC current without changing the inductance too
much. The effect would be that the bias will not be displaced by any
appreciable amount - DC resistance is about 400 Ohms, so a lot of current
must flow for a single volt to appear. You will nead 2 chokes - one for each
side of the push-pull output sections - no need for one per bottle.

One possible problem might be the impedance (or DC resistance) of the bias
supply if this is a negative voltage sent to the grids (relative to
0V/ground). this probably presents a DC resistance of about 10 to 50k, but a
couple of electrolytics of about 220 to 1000 microFarads should be enough to
stabilise the bias reference points - just allow them to be disconnected
when you are setting up the bias. You want a pretty long time-constant to
allow you to play your bit of overdriven (noise) without upsetting the
situation. In the limit, you could put in a couple of LM317s in a suitable
circuit to provide 30 to 40 V as solid as a rock, but well bypassed against
parasitics with all that inductance around.

If you don't like the idea of old SE OP TFs, you could ask Sowter for a
quote for a couple of 40 Henry chokes at about 250 Ohms (or less) - should
be easy. Normal swinging chokes are quoted at about 40H at 10mA (reducing to
2H at about 150mA), but they are probably too heavy and since we don't need
150mA current carrying capacity, we can get away with thinner copper, which
means a smaller window ... shorter magnetic path ... lighter lump of
metals.

I also like Turner Audio's use of 10 Ohm cathode resistors. This makes
setting the bottle current easier (than 1 Ohm) while limiting the current
drawn before the effect of bias and may save you cooking the OP TF. I would
also mean that an automatic cut-out could be fitted without too much
trouble - a 1N4148 (or a schottky for a higher reliability) from each
cathode to an op-amp set for (say 75mA per bottle through 10 Ohms gives
0.75V. Knock off the 0.6V (0.35V for the Schottkys) you first thought of for
the 1N4148s and you have 0.15 V (0.4V) to set as your theshhold to flip the
op-amp into energizing the relay which cuts off the HT (and locks the relay
on through a high resistance to HT -or the bias supply). There is also a
negligible power loss.

I am not sure whether you want to have separate bias pots for each bottle
if you are going to use 6 of them - one per side, with a common cathode
resistor for each side to measure the current through each triad might well
be easier in the long run. Remember that ultimately, you want equal currents
on each side at equvalent portions of the waveform. It does not matter that
the individual bottles are matched; what you want is a+b+c = c+d+e
(everywhere you can get it). Static biassing only guarantees it at a
quiescent state in any case.

With Turner Audio's 10 ohm resistors, you could also set up an op-amp to
compare a rectified voltage from each side and flash up a "reset bias"
alarm/lamp when things get too far out of kilter. A pot across the bottoms
of the 2 bias pots would enable (with a bi-colour warning LED) you to trim
the bias back into the reasonable area without resorting to measuring
equipment i.e on-stage (fiddle with it while playing, until the little
light goes off).

Well as you can see, I'm taking all this in slowly (probably too slowly for
my tastes) but it's really nice and educational and at the end of it,
there's a possibility of a nice reward. Hats off to this forum though for
being so helpful (ok with one exception) but I'd like to take the oportunity
to say that it's really well appreciated.

Thanks.
cb

"Adam Stouffer" wrote in message
...
Chris Berry wrote:
My initial theorem, which is useful insofar as if it is theoretically
possible, then there's a very good chance that I might act on it, asks
the
question "how light is it possible to design a kt88 based amp with at
least
200W of power (300W or 400W would be better for me though) for bass"


How about a pair or even quad of 811As running class B? You don't really
need something meant for hifi. A quad should get you a low enough plate
resistance to use cheaper transformer. A pair running class B will give
you 235 watts.

I'd stretch to ab2 but class B just seems to offend my sensibilities -
althout I'm sure there's nothing wrong with how it would sound though.
It's a sort of strange logic I've got. No-one builds an B class bass amp so
there might be a reason for it... I don't want to pay to find that one
out...
cb

Patrick Turner wrote:


to reach the same result for saturation as any E&I tranny.
A toroid with an area of 7,500 sq.mm would be rated for around
3 Kw for mains use.

It would be with some caution that I would advise anyone trying
to make a toroidal transformer for such high powers,
and high voltages, and I would first suggest that
the question of insulation is crucial with HV,
and perhaps a thouroughly oil filled pot be used for the HV tranny.

there is really no need for oil insulated transformers for such small
transformers with relatively low voltages.
Large transmitter power-supplies with 4500V/phase at 50-100KVA use just
air insulated, not potted transformers

Concerning a bass amp with 700W, 12 EL34 class B with 600V on the plates
should provide 600W, so 12 EL519 easily would do it, in that case I
would
use a autotransformer as the output tranny and feed the -HT at the
catodes,
a output toriodal transformer for such few windings should be no
problem,
anybody wth a winding machine for toroids can wind it.

Peter

"Patrick Turner" wrote in message
...


Chris Berry wrote:

"Patrick Turner" wrote in message
...
snip
Thanks for the informative post Patrick - There's a lot of information
there
and it will take time to digest....

To add a bit of background, I'm intending on using a fair few more watts
than 55!

The wattage isn't of huge concern here to begin with.
The turns per volt are main problem with mains trannies.
Even with two x 240 v primaries wound onto a toroid
you still would get 1.2 Tesla at 480v across the winding at 50 Hz.
it would saturate at 1.5 T at 40 Hz.
Better performance from a well made OPT would give
1.5 Tesla at 480v at 20 Hz, and there would be twice the turns,
ie, the equivalent of 4 x 240v primaries.



My initial theorem, which is useful insofar as if it is theoretically
possible, then there's a very good chance that I might act on it, asks
the
question "how light is it possible to design a kt88 based amp with at
least
200W of power (300W or 400W would be better for me though) for bass"

I have built 300w+ amps, and the details are at
http://www.turneraudio.com.au/htmlwe.../poweramps.htm

Amazing stuff - very pretty. How does one chose the paint colour? Personally
I'd take racing car green... taste eh?


The OPTs weigh near 20 Kgs, or 45 lb.
There is a 100 mm stack of 50 mm tongue material,
and this reduces the primary turns required to only 1,100.
There are 6 sec sections and 5 pri sections for a bandwidth
between 14Hz and 270 kHz, at 300 watts into 1.1k ohms a-a,
working with 12 x EH6550, using cathode bias, and Ea = 480v.

Not quite the kinds of weight I'm thinking about.


For a bass amp, you need some iron; its not an area where anyone else
ever skimps.

I'm hoping that the shift to toroidal transformers would drop the weight
signifficantly enough - without affecting quality too much.





To give you an idea as to why I need so much power, I'm currently using
a
2400W RMS solid state amp to power my bass rig so it should be able to
handle my speakers with ease...

So why not stick with SS?

Different tools for different jobs really. The PA amp is very heavy and very
powerful - but also sounds "modern" when combined with one of my cabinets in
a specific setting. The same cabinet (a 2x 10" + horn midrange) sounds
completely different when I bypass the midrange and use a 6dB low pass at
1500Hz - especially with a 50's 50W Eminent valve amp. Different again is
the use of my 15" cabinet which has just the right balance for the Eminent
10W amp - but the Eminent seriously lacks horsepower. I'd like to have the
valve sound at the PA amp's volume. I tried my Marshall 100W valve amp and
there just isn't the power there for the volume levels I've needed.




Anyway, back to your comments... I found your website most helpful and
am
still wading through your comments.
Plitron, afaik make transformers that are a little on the pricey side
and
way overengineered (at least 25% over) for my purposes.

Well I build for the hi-fi market where folks expect power amps to deliver
full power at 20 Hz into the rated load.

This means that for a given number of pri turns, the core must have
twice the weight of a tranny which is only required to get down to 40 Hz.
In my eyes, using the weight isn't overengineering.
But I see your point.


There are companies round here that wind to spec and for very reasonable
prices. - If I can wade through the theory...

I would have your specialist winder choose a 1,000 VA core,
and have him place 2 x 240v primaries on, then all your secondaries,
which I assume you are going to parallel, and then another 2 x 240v secs.

With a 1,000 VA mains tranny, the turns per volt might only be 1 turn per
volt,
so its only 240 turns.
960 pri turns would be OK if the core crss sectional area is say 50mm x
44mm.


For the sec, it depends on the load match you intend.
If the load match is 5k to 8 ohms, the Z ratio is 625 : 1
so a turn ratio is the square root of 625, so 25:1.
For 1.25k : 8 ohms, the ZR = 156 :1 so TR is thus only 12.5 :1,
so you'd need 77 secondary turns.
These could be in several paralleled windings,
or one winding around the toroid using quite thick wire,
so that to get low copper losses the sec wire DCR 0.4 ohms,
and also the DCR of the primary 48 ohms.
This will give power losses of less than 10% overall.
But for 5% losses, the wire dia has to be 1.41 times greater.


If we back up a second... Sowter in the UK make a 200W transformer for
KT88's (5 pairs for 400W) that's not toroidal and weighs 8.8kg (about
20lbs). In comparison, a plitron one for twice the power is 10.5kg , the
plitron one being at least 50% overweight.



To put it simply, without a toroidal OPT, I can't get close to my weight
aims and $500 for a Plitron transformer just isn't on the cards... maybe
getting a custom one from Plitron - but then again I'm in the same
ballgame...
http://www.plitron.com/PDF/PB/specs/pat4140-00.pdf
Is more than 50% overengineered for my purposes for instance and has a
canadial list price of $444 - add on import duties...

I didn't say Plitron were cheap.

The cost per watt for a 20 watt OPT is high, but you doing 300 watts,
and then the cost per watt has fallen.

A core rated for mains use of 1,000 VA at least is needed for
an audio tranny wanted for 300 watts bass use.

The cost of winding the 1,000 watt core with more turns suited to
an audio use will only be greater because more copper, insulation,
and labour is used. But the wire used for the primary will be thinner.

Well, I've 2 avenues - one being the standard transformer winders in
Germany. The other is Mercury magnetics in the US who I believe know what
they do well.


One thing for sure, for getting good value, your tranny needs
some professional design work done to get the best.

I wouldn't use a toroidal because of the saturation problem.
The U of the toroid GOSS can be around 40,000 today, due to adavnces in
materials.
The same material used in E&I lams could give about 17,000 in an E&I core.
The E&I use is the equivalent of a very slim air gap.
I now use E&I lams for all my trannies, and its U max is 17,000;
it is the finest material I can get, made in Oz at Newcastle, NSW.
The thd is 1/20 that of NOSS.
In 1955, RDH4 referred GOSS max U at 5,000, E&I lams.
But plain old half priced NOSS is about 3,500 max in E&I lams.
And to my mind, NOSS would be better to use.
The thd generated by NOSS is a much higher than GOSS when away from
voltage levels which cause saturation, but nevertheless its not excessive,
and still a lot less than that produced by the tubes,
and some of my best sounding amps use NOSS cores.
The HF core losses are negligible.


Toroidal is the only way I'd go ahead - with or without laser cutting
though.
Unfortunately, I live on the 4th floor of a block of "vintage" (protected)
flats with no lift.
So it's basically a question of weight and performance. Less than 200W
wouldn't be useful.




If you know of web resources that can help me calculate the design
parameters for a toroidal OPT precicesly enough, I can get a 700VA made
up
locally for under $100 - surely that core is enough for an OPT?

The design above which I mentioned using 960 turns on a 1,000 VA core
should be able to be pushed to give 700 watts at mid frequencies,
but perhaps saturation will occur at 40 Hz or higher F.
The number *MUST* be worked out before winding a single turn.

We need to know exactly what design of amp you are building,
including all the operating and supply voltages.

I'll try my best to provide the information as we go along.
Working with 6 KT88's with 600V on the HT.
According to the spec he
http://www.mif.pg.gda.pl/homepages/f...35/6/6550A.pdf
300V would be well within spec for 3 pairs in AB1. AB2 would probably be
closer to what I'm after in terms of sound.
Essentially, I would like to use it as a slave amp and power it initially
with my solid state preamp so as to be able to use any number of different
preamps with the amplifier.



The winder needs to have a full specification before he starts.


Thanks once more for the time and effort taken in supplying me with all
the
info.
cb

The info supplied isn't enough to start spending that $100.

And don't be sore if the cost is $200.


If the cost is even $300, that would be about half the price of importing it
from canada - although I do have some contacts there that could help me with
customs....
While we're specifying things here, there are some "project deadlines" to
consider.

3 months - setting the design parameters, feasibility testing (is it worth
going ahead basically)

+6 months: prototyping - basically getting it working without the final
chassis (probably on a sub-chassis) so as to troubleshoot wiring and
component "issues".

+3 months - finishing - getting the final layout onto a stable chassis,
machining, painting all done and having a "final product".

I won't be disapointed if I have to abandon after 3 months. The knowledge
rewards are such that it's very likely that I'll just be happier for it.

The closest thing to what I'd like to build is the ampeg SVT CL or svt pro
which uses 6 kt88's for 300W at 80lbs - a completely impractical proposition
for someone in my position...

The easiest thing would be to copy one of these:
http://www1.korksoft.com/~schem/ampe...eramp6550a.pdf
and go for the toroidal option.

Thanks guys.
cb

"Patrick Turner"


Below, Allison insults Yves and tries to lead us all astray.


** Below the Turneroid posts utter lies like the criminal he is.



A 2 x 115v winding on a mains toroidal is usually set up
for 1.2Tesla for the 230v, ie, with 115v across each of two 115v windings
in
series.
If the load is 5k, you get 10.6 watts.


** Just as I said and Yves denied.


BUT, the maximum B is around 1.6 Tesla before severe saturation and
distortion
occurs,
and with 230v, that occurs at 37.5 Hz.


** The lowest note a bass guitar can produce is 42 Hz - but a ****wit
like the Turneroid has no idea.



If we wanted 50 watts,


** If pigs could fly ........ the Turneroid would own a airline.



So the only bum thinking and bull**** is in Phil Allison's mind.


** Everything the lying Turneroid posts is stinking bull****.



There is some reason behind what Yves has said,


** Yes, but it none of it applies to a toroidal transformer.



Chris Berry originally asked us all about using a mains tranny.



** Bull**** - he was referring to a toroidal using a similar core to
mains types.



He has since said in a following post that he wanted to make 700 watts,


** Bull**** - he wants to make a 200 watt tube amp for his bass guitar.


For under A$250 a suitable toroidal can be supplied by local winders
given a simple spec to follow.



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

Chris Berry wrote:

"Patrick Turner" wrote in message
...
Chris Berry originally asked us all about using a mains tranny.
He has since said in a following post that he wanted to make 700 watts,
not just 50 watts.

Well 700W wound be nice....
Down to specifics though, 3 pairs of kt88's would do me fine.
class AB2, 600V on the annodes that would give about 360- 400W no?

I thought you mentioned 700 watts in a previous post.

I may have drawn the incorrect conclusion from

"My initial theorem, which is useful insofar as if it is theoretically
possible, then there's a very good chance that I might act on it, asks the
question "how light is it possible to design a kt88 based amp with at least
200W of power (300W or 400W would be better for me though) for bass"

To give you an idea as to why I need so much power, I'm currently using a
2400W RMS solid state amp to power my bass rig so it should be able to
handle my speakers with ease..."

700 watts is only 3dB louder than 350 watts.

If you are to use only 6 x KT88 or 6550, and go for 400 watts,
then that's 133 watts per pair of output tubes, which
is about the maximum amount.
I wouldn't do this because of reliability issues, knowing
as I do how guitarists routinely over drive their amps thus producing
up to 600 watts with 40% thd from an amp which clips with a sine wave at 400
watts.

8 x KT88/6550 would be the minimum IMHO.
With Ea = 550v, and fixed bias you should get around 400 watts to the rated
load,
more for a lower load, and less for a higher load.
The voltage swing into the rated primary load would be about 600v
so for 350 watts the load would be around 1.1k a-a.

Let us assume you used a toroidal core with a cross sectional area
of 100mm high with a build up 50mm.
Assume the highest v a-a is to be 600v.
Assume that 20 Hz operation is wanted since it is prudent even though
you say you only need to go down to 40 Hz.
Assume a max allowable B = 1.5 Tesla.
The P turns = 22.6 x 600 x 10,000 / ( 1.5 x 50 x 100 x 20 )
= 904 turns.

I'd use 1,000 turns, and about 0.7 mm dia wire is OK.

The impedance ratios you want go from 1.6 ohms to 8 ohms.

So quite a few windings are needed if you want the same low
losses at 1.6 ohms as at 8 ohms.

1,100 ohms: 1.6 ohms is 687.5 :1,
so a turn ratio of 26:1 for 1.6 ohms is needed.

There would be 6 sections of 38 turns each, which could be paralleled for 1.6
ohms.
If 3 + 3 windings were parallel/seriesed, then the match would be to 6.4 ohms.

I would suggest about 1.5 mm dia wire be used.

Alternatively, if you had 3 x 38 turns and 6 x 19 turns, the windings could be
arranged
so that the above 1.6 and 6.4 ohms are available,
but also 3 x (38 + 19) in parallel with 19 + 19+ 19,
so you get 4 x 57 all in parallel for 3.6 ohms.

These figures could be rounded up a bit so you had secondaries = 40 turns and 20
turn windings,
so you'd get
TR = 25:1, 1,000t : 40t, giving 1.1k to 1.8 ohms,
TR = 16.6:1, 1,000t : 60t, gives 1.1k to 3.97ohms,
TR = 12.5:1, 1,000t : 80t gives 1.1 k to 7.2 ohms.

The switching of the windings for impedance matching needs to be done
with a very high current multipole switch mounted right on the transformer
terminal board.
The total number of terminations to allow pentode or UL operation
and to allow for 9 secondary windings would be 5 + 18 = 23 terminals.

Most custom winders will vomit all over you when you show them what you want
them to
do, including the provision of a nice termial board, all neatly laid out and
labelled,
fully tested, etc.
Most are right out of their depth when asked to do such things.

For a toroidal, the first 500 pri turns can be wound on first, then all the
secondaries,
then the next 500 pri turns.
This means lots of sec turns have to be fed out through the second lot of 500 P
turns,
which causes the vomiting.

Every section and layer has to be isolated from every other, so a winder needs
to know
what he's doing lest he get confused, which is very easy.

Far easier would be a bobbin wound OPT,
preferably using a 75 mm stack of 62.5 mm tongue E&I laminations,
and for your purposes plain NOSS would do.

At least the same same numbers of turns would be used, but some careful
calculations are needed
for wire size to fit the traverse width of the bobbin. The turns could be
increased,
but not decreased.

The available winding area in the widow is 90mm long x 28mm high.

The arrangement would be so that the P is divided into 5 sections
of 2 layers each, and if the P wire is 0.7 copper dia, then allowing for
insulation enamel,
there would be 117 turns per layer.

The P would thus have 10 x 117 turns = 1,170 turns.

The S would consist of six sections, 3 of 48 turns in the one layer,
and 3 of 2 x 24 sections, and wire size would be 1.6 mm copper dia, about 1.7
oa.

The insulation between P&S = 0.8 mm and between P&P layers = 0.05mm,
so total wind height can be calculated,

P is 10 x 0.76,
S is 6 x 1.7,
P to S ins 10 x 0.8,
P to P ins 5 x 0.05

Total = 26.o5 mm, which will fit into the avaiable winding height.
In fact, the insulation between P&S can be increased from 0.8 to 1 mm
and I suggest stiff mylar ( polyester ) sheeting be used.

Bandwidth at 600 v a-a would be at least 20 Hz to 200 kHz.




That basically concludes what's going in to the OPT but as to what I'd like
out, that would be a bit more complicated wrt ideal impedances.
Ideally, I'd like 2, 2.66, 4 and 8 ohm windings/combinations... so 3 x 4ohm
taps would do fine - 4 would be better so long as they can handle the power.
The reason being that I have both 4 and 8 ohm speaker cabinets and am likely
to use a second 4 ohm cabinet in future. 1.6 ohms would also be nice to
have - but not essential mind you.

I hope the above designs allow you proceed.




I have asked him for details of his proposed amp, so we could
design a tranny right here on the group should he wish to do so,

Sorry, I didn't get around to seeing that offer. I'll take you up on it
gladly.

for the benefit of all those here interested in building tube amps.
There are many ways to make 700 watts.
One could use a quad of 813 with a 2,500 volt supply,
for mainly class B operation, ie, low% of class A,
with a high voltage swing, low current swing.

Patrick, for some things I want to stay within "convention" for guitar amps.
Since weight's a priority, as is a fairly clean sound, I think I'll take the
ab2 kt88 version as being a good compromise and save some weight with the
transformers.

Its impossible to make a real lightweight 350 watt tubed bass amp.

The way around that is to have two chassis, with PS on one, and the amp module
and OPT on the other.
Each will weigh around 20 Kgs+ or over 45 Lbs.

There has to be a special power cord between the amp and PS,
which for a roadie is a problem because its something else which can go
wrong, so the power cord has to be a very rugged 5 wire cable, like they use on
mobile cranes,
and with a milspec plug and socket.
You need to convey +550v B+, 0V, two heater wires, and the bias supply.



Working out the figures in terms of weight, using toroidal transformers I
should be able to get the transformers for the amp to weigh in at under 9kg
or 20lbs - making a 20kg amp a distinct possibility.
Just to put things into context a Marshall 50W guitar amp weighs 39lbs - I
should be able to build this under 30lbs at a guess.

My 300 watt monos weigh 50 Kg for each channel; the amp chassis is
25 Kg, and the PS is 25 Kg.
I use a welded steel chassis for the amp.
It cannot be flimsy for road use because if it drops, the weight of the trannies

will deform any thin steel chassis.

Toroidals are best potted, so their weight on the windings is evenly
distributed.

You can work out the weight of the cores by calculating their volume
for the core, and using 8 grams per cc as the density.



That's a jump from 1.2W/lbs to 12W/lbs - a signifficant weight advantage.

Cost per watt plummets as the amp gets more powerful.



Some avenues I've taken a quick look at so far include a few unusual
options.
One quite insane one but probably feasible (safety wise there are doubts but
I think the "killer" would be noise) would be to get the HT without a
transformer at all. Just voltage doublerss would give me 500V round here
(220V) but some kind of soft start using relays to wire the thing up so live
and neutral are the right way round.

AAAAAHHHHH, don't ever do this.

Its unsafe!.

And you will have terrible hum problems, and still you will need a hefty
transformer for the heaters and bias.



Another not so insane but probably too good to be true would be to take a
toroidal core and get someone with laser cutting facilities to cut afine
"crack" into the core itself. so long as the "crack was smaller than the
wire diameter, this wouldn't cause problems winding the transformer
(although a solution to that wouldn't be too difficult either).

You mean a cut in the core. Cores can be supplied by some suppliers witht the
cut
already there, ie, an air gap.

I don't think that you will get much significant weight advantage
betwen using a massive toroid or an E&I lam tranny each of which requires the
same
cross sectional iron area within the turns, for the same turn count.



I have a good partner in crime here - my father - who has considerable
experience with valves albeit mainly on warships and radio - but enough to
stop any major damage. He's 100% original and verging on vintage (gotta love
parents like that) and I've sent a most of the information you've sent my
way for his processing.

I bet he thinks toroidals are poofy rubbish compared to "real transformers".



Here's one of his deepest darkest responses:

Just an idea (which, incidentally will add a little weight ...)

Since the problem with fixed bias P-P PA stages with Negative feedback is
what happens when they are overdriven - I forget the link you sent me (put
it in here if you pass this on), how about putting a choke in place of the
grid leak. The problem is the rectified grid current not having a discharge
path from the grid, building up an appreciable charge on the grid, pushing
it into grid current operation - to my mind BAD for business - unless you
sell bottles.

Fixed bias with RC coupling is best with guitar amps, and the over loading
results in the grid current charging up the coupling caps, thus
biasing the tubes off, and reducing anode current in severe bursts of
severe overdrive. This protects the tubes from excessive dissipation.
Basically, a class aB1 amp behaves as a class C amp when severly overdriven
by a guitarist.
The NFB causes the overdrive to be even more severe than without NFB, but the
driver stage just stalls,
since there is not ablity to drive into grid current, and possibly
wreck the tubes.

The over driven tube amp is basically a square wave producer, and the sound is
generated
by the speaker driven by this very distorted wave.
Its a very primitive process.




The choke will give a low impedance (instead of 100 to 500k resistor) path
to 0V/ground for the DC generated by the grid current as the Amp passes into
overdrive . A cheap choice would be a single ended OP transformer for (say)
2.5 W, with the secondary removed (quite easy since the Secondary is
normally the outside winding). These TFs have an air gap which means that
they can handle the small DC current without changing the inductance too
much. The effect would be that the bias will not be displaced by any
appreciable amount - DC resistance is about 400 Ohms, so a lot of current
must flow for a single volt to appear. You will nead 2 chokes - one for each
side of the push-pull output sections - no need for one per bottle.

IST coupling is fine in itself, but they tend to add time constants into the
circuit and thus
reduce stability when FB is applied.
They are used where AB2 operation is needed to push a tube to rail clipping
before grid
current flows.
With normal KT88/6550, the rail clipping occurs well before onset of grid
current,
so no need for any IST or low impedance drive.

The main issue is the control of the bias after recovery from severe over drive,

so less than 50k should be used for biasing each output tube grid.

Careful driver design should be considered, say a couple of EL84 or 6V6 in
triode
will do.



One possible problem might be the impedance (or DC resistance) of the bias
supply if this is a negative voltage sent to the grids (relative to
0V/ground). this probably presents a DC resistance of about 10 to 50k, but a
couple of electrolytics of about 220 to 1000 microFarads should be enough to
stabilise the bias reference points - just allow them to be disconnected
when you are setting up the bias. You want a pretty long time-constant to
allow you to play your bit of overdriven (noise) without upsetting the
situation. In the limit, you could put in a couple of LM317s in a suitable
circuit to provide 30 to 40 V as solid as a rock, but well bypassed against
parasitics with all that inductance around.

LM317 do not belong in any tube amp whatsoever, IMHO,
since thay are low voltage chips, and easily zapped.
The bias supply is best left unregulated, except via the transformer winding,
and low resistance dividers.


If you don't like the idea of old SE OP TFs, you could ask Sowter for a
quote for a couple of 40 Henry chokes at about 250 Ohms (or less) - should
be easy. Normal swinging chokes are quoted at about 40H at 10mA (reducing to
2H at about 150mA), but they are probably too heavy and since we don't need
150mA current carrying capacity, we can get away with thinner copper, which
means a smaller window ... shorter magnetic path ... lighter lump of
metals.

The only choke needed in the amp apart from a possible plate choke for the
LTP driver is a power choke for the B+ supply.



I also like Turner Audio's use of 10 Ohm cathode resistors. This makes
setting the bottle current easier (than 1 Ohm) while limiting the current
drawn before the effect of bias and may save you cooking the OP TF. I would
also mean that an automatic cut-out could be fitted without too much
trouble - a 1N4148 (or a schottky for a higher reliability) from each
cathode to an op-amp set for (say 75mA per bottle through 10 Ohms gives
0.75V. Knock off the 0.6V (0.35V for the Schottkys) you first thought of for
the 1N4148s and you have 0.15 V (0.4V) to set as your theshhold to flip the
op-amp into energizing the relay which cuts off the HT (and locks the relay
on through a high resistance to HT -or the bias supply). There is also a
negligible power loss.

I have active protection circuits driven by the signals from the 10 ohm Rk.
If the DC in any one or all of the 10 ohms ever exceeds twice the bias current
for longer than 4 seconds,
the B+ is turned off by a relay.
That suits my hi-fi situation, but it does guard against the errors by the
russians in their tube factories.


I am not sure whether you want to have separate bias pots for each bottle
if you are going to use 6 of them - one per side, with a common cathode
resistor for each side to measure the current through each triad might well
be easier in the long run.

Individual biasing when fixed bias is used is essential. Otherwise its a hassle
to seek
an octet of matched tubes.
For a bass guitarist on the road, freedom from needing matched tubes would be a
blessing,
so if a tube blows, pull it out, plug any other in, rebias, and tou are away
again.
Matched sets don't stay matched, and after a year on the road, the tubes
will each require very different grid voltages to give the same plate currents.


Remember that ultimately, you want equal currents
on each side at equvalent portions of the waveform. It does not matter that
the individual bottles are matched; what you want is a+b+c = c+d+e
(everywhere you can get it). Static biassing only guarantees it at a
quiescent state in any case.

True, but the man on the road is unlikely to ever hear any benefit of
dynamic transconductance equality each side of the PP circuit.
The inequality will only marginally increase the thd,
and probably warm the sound, as the imbalance distortion is 2H.
Don't worry, she'll be right!
You *must* have equal static current bias at least to begin with.



With Turner Audio's 10 ohm resistors, you could also set up an op-amp to
compare a rectified voltage from each side and flash up a "reset bias"
alarm/lamp when things get too far out of kilter.

No need for opamps, a circuit with a couple of discrete transistors
and an SCR is all that's needed to create an "error signal" to power a relay off
+12v.


A pot across the bottoms
of the 2 bias pots would enable (with a bi-colour warning LED) you to trim
the bias back into the reasonable area without resorting to measuring
equipment i.e on-stage (fiddle with it while playing, until the little
light goes off).

Yes, also doable, but really one red-green led is needed per output tube,
and soon things get complex.
On stage at a gig, the red or green of leds will not be noticed,
and all that matters is protection of the OPT against bias failure.



Well as you can see, I'm taking all this in slowly (probably too slowly for
my tastes) but it's really nice and educational and at the end of it,
there's a possibility of a nice reward. Hats off to this forum though for
being so helpful (ok with one exception) but I'd like to take the oportunity
to say that it's really well appreciated.

The is quite a bit to be considered when building any amp.

Patrick Turner.



Thanks.
cb

Chris Berry wrote:

"Adam Stouffer" wrote in message
...
Chris Berry wrote:
My initial theorem, which is useful insofar as if it is theoretically
possible, then there's a very good chance that I might act on it, asks
the
question "how light is it possible to design a kt88 based amp with at
least
200W of power (300W or 400W would be better for me though) for bass"


How about a pair or even quad of 811As running class B? You don't really
need something meant for hifi. A quad should get you a low enough plate
resistance to use cheaper transformer. A pair running class B will give
you 235 watts.

I'd stretch to ab2 but class B just seems to offend my sensibilities -
althout I'm sure there's nothing wrong with how it would sound though.
It's a sort of strange logic I've got. No-one builds an B class bass amp so
there might be a reason for it... I don't want to pay to find that one
out...
cb

Many tube amps are almost class B amps, because the cut off in one half of the
PP circuit
occurs after only a few watts of class A have been made.

I have heard some quite nice 400 watt amps, one of which used 8 x EL34
with a 900v anode supply, 450v screen supply, and only 17 mA of idle current
for each tube.
It didn't make much class A, and it tended to be a little unreliable.
But with 12 dB of NFB it sounded passable for PA.
It filled a hall with 300 folks easily, at a cultural festival.
Used as a guitar amp, smoke might have been encountered.

Patrick Turner.

Peter Völpel wrote:

Patrick Turner wrote:

to reach the same result for saturation as any E&I tranny.
A toroid with an area of 7,500 sq.mm would be rated for around
3 Kw for mains use.

I get nervous around anything with 2,000v,
and to have an amp on stage at a gig with 2,000v would be "courageous",
bearing in mind spillage of beers...............



It would be with some caution that I would advise anyone trying
to make a toroidal transformer for such high powers,
and high voltages, and I would first suggest that
the question of insulation is crucial with HV,
and perhaps a thouroughly oil filled pot be used for the HV tranny.

there is really no need for oil insulated transformers for such small
transformers with relatively low voltages.
Large transmitter power-supplies with 4500V/phase at 50-100KVA use just
air insulated, not potted transformers

Concerning a bass amp with 700W, 12 EL34 class B with 600V on the plates
should provide 600W, so 12 EL519 easily would do it, in that case I
would
use a autotransformer as the output tranny and feed the -HT at the
catodes,
a output toriodal transformer for such few windings should be no
problem,
anybody wth a winding machine for toroids can wind it.

Peter

The drive voltage to the grids would be rather high.

But yes, and auto tranny cathode to cathode is OK.
But the load seen by the tubes must still be the same as for plate loading,
lest
the dissipation exceed safe limits.

Patrick Turner.

"Patrick Turner"

Assume that 20 Hz operation is wanted since it is prudent...


** Turneroid bull crap.


For a toroidal, the first 500 pri turns can be wound on first, then all
the
secondaries, then the next 500 pri turns.


** More Turneroid lies.


Far easier would be a bobbin wound OPT,


** Even worse Turneroid lies.



I hope the above designs allow you proceed.

** Not down that path in a fit.



Its impossible to make a real lightweight 350 watt tubed bass amp.


** Biggest Turneroid lie yet.


The man is a fool and a MENACE !!!!!





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

Chris Berry wrote:

"Patrick Turner" wrote in message
...


Chris Berry wrote:


snip,



If we back up a second... Sowter in the UK make a 200W transformer for
KT88's (5 pairs for 400W) that's not toroidal and weighs 8.8kg (about
20lbs). In comparison, a plitron one for twice the power is 10.5kg , the
plitron one being at least 50% overweight.

200 w can be done using a tranny of 8.8 Kgs. The question is losses.
In my trannies, I like no more than 6% copper losses.
If the losses are allowed to be 12%, then the copper size
can be smaller, so a smaller core can be used, because the windings will fit
onto
the core, and more turns can be used, to compensate for the smaller core size.

I prefer the larger core, fewer turns, lower losses, and weight isn't an issue.
But where weight is an issue, then you pay for the convenience with
power wasted as heat in the OPT.



snip,


The cost of winding the 1,000 watt core with more turns suited to
an audio use will only be greater because more copper, insulation,
and labour is used. But the wire used for the primary will be thinner.

Well, I've 2 avenues - one being the standard transformer winders in
Germany. The other is Mercury magnetics in the US who I believe know what
they do well.


One thing for sure, for getting good value, your tranny needs
some professional design work done to get the best.

I wouldn't use a toroidal because of the saturation problem.
The U of the toroid GOSS can be around 40,000 today, due to adavnces in
materials.
The same material used in E&I lams could give about 17,000 in an E&I core.
The E&I use is the equivalent of a very slim air gap.
I now use E&I lams for all my trannies, and its U max is 17,000;
it is the finest material I can get, made in Oz at Newcastle, NSW.
The thd is 1/20 that of NOSS.
In 1955, RDH4 referred GOSS max U at 5,000, E&I lams.
But plain old half priced NOSS is about 3,500 max in E&I lams.
And to my mind, NOSS would be better to use.
The thd generated by NOSS is a much higher than GOSS when away from
voltage levels which cause saturation, but nevertheless its not excessive,
and still a lot less than that produced by the tubes,
and some of my best sounding amps use NOSS cores.
The HF core losses are negligible.


Toroidal is the only way I'd go ahead - with or without laser cutting
though.
Unfortunately, I live on the 4th floor of a block of "vintage" (protected)
flats with no lift.
So it's basically a question of weight and performance. Less than 200W
wouldn't be useful.

Fair enough.
Gee, 4 floors with no lift would kill me, carrying anything I've made....






If you know of web resources that can help me calculate the design
parameters for a toroidal OPT precicesly enough, I can get a 700VA made
up
locally for under $100 - surely that core is enough for an OPT?
I'll try my best to provide the information as we go along.

snip,


Working with 6 KT88's with 600V on the HT.
According to the spec he
http://www.mif.pg.gda.pl/homepages/f...35/6/6550A.pdf
300V would be well within spec for 3 pairs in AB1. AB2 would probably be
closer to what I'm after in terms of sound.
Essentially, I would like to use it as a slave amp and power it initially
with my solid state preamp so as to be able to use any number of different
preamps with the amplifier.

200 watts is doable from a sixpack of KT88/6550.

BTW, EH 6550 seem to be exactly yhr same as EH KT88.

NOS jan green lettering GE6550A are regarded as the best 6550 around,
but to me they are just another 6550.

But 400 watts is a bit much.




The winder needs to have a full specification before he starts.


Thanks once more for the time and effort taken in supplying me with all
the
info.
cb

The info supplied isn't enough to start spending that $100.

And don't be sore if the cost is $200.


If the cost is even $300, that would be about half the price of importing it
from canada - although I do have some contacts there that could help me with
customs....
While we're specifying things here, there are some "project deadlines" to
consider.

3 months - setting the design parameters, feasibility testing (is it worth
going ahead basically)

+6 months: prototyping - basically getting it working without the final
chassis (probably on a sub-chassis) so as to troubleshoot wiring and
component "issues".

+3 months - finishing - getting the final layout onto a stable chassis,
machining, painting all done and having a "final product".

I won't be disapointed if I have to abandon after 3 months. The knowledge
rewards are such that it's very likely that I'll just be happier for it.

The closest thing to what I'd like to build is the ampeg SVT CL or svt pro
which uses 6 kt88's for 300W at 80lbs - a completely impractical proposition
for someone in my position...

The easiest thing would be to copy one of these:
http://www1.korksoft.com/~schem/ampe...eramp6550a.pdf
and go for the toroidal option.

Thanks guys.
cb

I think you have to draw up a complete list of the parts you have to source,
and then allow for months of work, if this is your first amp.

Best of luck.

Patrick Turner.

What would be a good spec for a toroidal 200 watt OPT?

AEM cores of Sth Aus tell me that a toroid made with 100 mm strip width,
so its 100mm high, and with a build up of 50mm with a centre hole of 100 mm
would weigh 17.7 Kgs and cost aud $145, plus 10% GST and delivery, so about
$180 all up, and about $10 per Kg is the going rate for GOSS.

To compare with E&I laminations with the same core leg area you need
a 100 stack of 50 tongue material, and this would weigh 12 Kgs.

So for the same cross section of iron, the weight for the E&I tranny is far less
than a toroid.

But with the toroid, the build up could be 25mm instead of 50mm,
and the the internal hole dia of 100 mm maintained, so that then the
weight would be 9.8 Kgs.

Since Afe is 1/2 that mentioned above, you need twice the turns,
but the winding should still fit around the core.

If Vmax a-a of the amp is 600v a-a rms,
and we want Fsat at 20 Hz, and at 1.6 Tesla, then
Np = 1,695 turns, or around 1,700.

For a load of 1.5k to suit 6 x KT88/6550,
the DCR of the P winding should be less than 2.5% of the 1,5k,
so that's 37 ohms, and my wire tables tell me to use 0.55 mm copper dia wire.

The match to 2.0, 4.5 and 8 ohms is done using
a secondary of 62, 93, or 124 turns respectively.
So 3 windings 62 turns and 3 of 31 turns give
4 x 62t paralleled for 2 ohms,
3 x 93t paralleled for 4.5 ohms,
2 x 124t paralleled for 8 ohms.
only one winding of 31 turns is not used with the 8 ohm arrangement.

If the inside dia of the toroid with 1/2 the primary on is 80 mm,
then the distance around is 3.14 x 80 mm = 251 mm,
and if there are 279 total secondary turns, then 0.8 mm dia wire
would be used for making the sec with just one layer.
But the losses would be well above 5%, and so
we should use two layers of secondary, using 1.5mm dia wire,
so that the sec turns fill the distance around the toroid twice, but without
overlapping into a 3rd layer, and losses would be just less than 5% for the sec.

The total winding losses therefore should be less than 10%.

The second 1/2 of the primary is wound over the top of the secs.

Always take a bucket and mop to the transformer winder when you tell him/her to
wind
such a transformer for a price of less than aud $250, because he'll spew up
when you tell him.
However, the material costs of the 10 Kg core would be around $100,
and about $30 for the wire, and possibly $30 for the insulation and terminals,
but potting, termination board, varnishing and the resin would all add up,
and the labour alone would be at least 5 man hours total,
and at $50 per hr for skilled labour using a costly winding machine for some of
it,
avacuum chamber and handling toxic chemicals, expect a bill of at least aud
$450.

Asking for a small air gap of say 0.02mm in the core would reduce its tendency
to saturate so easily with a DC offset, but it will cost extra.
The transformer with a gap has a fundemental structural weakness,
and I suggest potting the compete transformer after carefully vacuum
impregnating with epoxy varnish will make the tranny less likely to
have its bond across the air gap break, and thus allowing the gap
to become larger than intended, or to chatter with applied signals.

The max U of the material might be as high as 20,000 with no gap,
but AEM have yet to confirm this.

The maximum Lp would be 464 Henries, somewhat less than could be achieved
with an E&I tranny with the same U and Afe, because the magnetic path
length of the toroid is longer than the E&I material.
The U will fall at low levels, but still we'd have 100H,
so the 3 dB pole with a load of 1.5k with pentode drive is 2.4 Hz.

I suspect the HF response would be excellent, but
serious DIYers would specify that the
windings be interleaved so there is a P S P S P arrangement of symetically
laid out layers, instead of the simple P SS P set up so far described.

I hope this is of some use to others including our Chris Berry.

Patrick Turner.

No need to to reply to Allison's posts which merely
say I am a liar, etc, etc, etc.

He offers no alternatives to my design ideas, complete with *all* the
details.

But its Easter, and the man likes to act like a real dumb bunny.

Patrick Turner.

"Patrick Turner"

What would be a good spec for a toroidal 200 watt OPT?


** The Turneroid moron has no damn idea whatever.


AEM cores of Sth Aus tell me.......



** All damn lies, they did not give any such spec for a 200 watt OT.





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

"Patrick Turner"
....
No need to to reply to Allison's posts .....


** The Turneroid CANNOT make any reply.


which merely say I am a liar, etc, etc, etc.


** Nothing much else needs to be said about a congenital liar, criminal
threat maker, slanderer, libeller ......



He offers no alternatives to my design ideas, complete with *all* the
details.



** When and if the OP asks me I will give him some figures he can use to
instruct a toroidal winder.


OTOH YOU can go to hell and burn.





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

"Yves"


IMHO, an output tranny for 500W, 1.2T at 40Hz will weight 20Kg, EI or
toroid
doesn't make large difference.



** A 500 watt toroidal OT wound for pp use with 40 Hz full power
capability would weigh 7 kg - at most.

Are you interested in facts at all Yves or do you just prefer to mentally
masturbate with your wildest fantasies ?????




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

"Phil Allison" wrote in message
. ..



** When and if the OP asks me I will give him some figures he can use to
instruct a toroidal winder.


Go ahead Phil, I'd like to see a different take on it and your figures for a
toroidal usable in the ampeg svt circuit.
cb

"Chris Berry" .


Go ahead Phil, I'd like to see a different take on it and your figures for
a
toroidal usable in the ampeg svt circuit.



** Hey ****** - that was NOT your original request for a 4 x6550,
200 watt amp with B+ of maybe 600 .





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

"Peter Völpel" wrote in message
...

..............

Concerning a bass amp with 700W, 12 EL34 class B with 600V on the plates
should provide 600W, so 12 EL519 easily would do it, in that case I
would
use a autotransformer as the output tranny and feed the -HT at the
catodes,
a output toriodal transformer for such few windings should be no
problem,
anybody wth a winding machine for toroids can wind it.

Peter

Hey !

Synthesizing a bit, there is perhaps here a path to explo
-Use TV sweep tubes that could run fine in AB2 with low Z load.
-Use no HV tranny, direct mains rectifier ( but input and output trannies !
Insulated box, chassis, buttons...etc.).
(Doubling 230V mains gives more than 600V, of course, filaments and bias
need an small auxiliary tranny)
-Specify the OPT for 40 Hz rather than 20 (There are a lot of infos below
40Hz from a bass, but there are at lower levels).

IMHO, an output tranny for 500W, 1.2T at 40Hz will weight 20Kg, EI or toroid
doesn't make large difference.

In the Ampeg schematic, (alas no voltages noted) it's clear that the 6 x
6550 are hardly driven in AB2.
The cathode follower 12BH7 driver insure lo DC resistance in the grids of
the output tubes while not using interstage tranny here.
This is not common for hi fi rigs (why ?) but right for this project.

The net result is 500W at less than 30 Kg

Yves.

"Phil Allison" wrote in message
u...

"Chris Berry" .


Go ahead Phil, I'd like to see a different take on it and your figures
for
a
toroidal usable in the ampeg svt circuit.



** Hey ****** - that was NOT your original request for a 4 x6550,
200 watt amp with B+ of maybe 600 .


Does that one provide a specific challenge? well OK for 4x6550 then - up to
you - I don't mind. 6x would be nicer though.
cb