Since it's hard to find chokes, I was wondering if a power transformer
or audio transformer can be used for one. I need a couple with about
0.5 henry at least 1 amp. Thanks

David R Brooks wrote:

In most applications, chokes carry a heavy DC current. If you put this
through a transformer (unmodified), you will likely saturate the iron
core.
Chokes usually have an air-gap in the magnetic circuit, to prevent
saturation. You may be able to experiment with altering your
transformer in this way. The air gap acts as a "resistance" in the
magnetic path, & reduces the flux to a level the core can handle. Of
course, it likewise reduces the inductance.


You can connect the secondary and primary in series in such
a way that they add more inductance. Not a lot more, but
as inductance goes up by the square of the number of turns,
it is significant. if it's a 12V secondary and 120V primary,
the inductance would go up 1.2 times.

"gojamo"...
Since it's hard to find chokes, I was wondering if a power transformer
or audio transformer can be used for one. I need a couple with about
0.5 henry at least 1 amp.


** Is that 1 amp AC or DC ??

What series resistance is acceptable ?




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

Phil Allison wrote:
"gojamo"...
Since it's hard to find chokes, I was wondering if a power
transformer
or audio transformer can be used for one. I need a couple with
about
0.5 henry at least 1 amp.


** Is that 1 amp AC or DC ??

What series resistance is acceptable ?




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

1 amp DC. No more than a couple of ohms. 0.5 henry preferred, but 0.3
henry acceptable. Thanks

"gojamo"

Phil Allison wrote:

Since it's hard to find chokes, I was wondering if a power
transformer or audio transformer can be used for one. I need a couple
with
about 0.5 henry at least 1 amp.


** Is that 1 amp AC or DC ??

What series resistance is acceptable ?


1 amp DC. No more than a couple of ohms. 0.5 henry preferred, but 0.3
henry acceptable.


** For a power tranny to have a *primary resistance* of 2 ohms means it is
huge - 200VA size if 120 volt, 600 VA if 240 volt !! The secondary
winding is the one to go for then - something of about 30 VA and 20 volts
might be about 2 ohms.

However - you will have to pull all the laminations out and re-stack them so
the Is and the Es are together and create a small air gap. Something like
0.5 to 1mm would be in the ball park.




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

Phil Allison wrote:

"gojamo"

Phil Allison wrote:

Since it's hard to find chokes, I was wondering if a power
transformer or audio transformer can be used for one. I need a couple
with
about 0.5 henry at least 1 amp.


** Is that 1 amp AC or DC ??

What series resistance is acceptable ?


1 amp DC. No more than a couple of ohms. 0.5 henry preferred, but 0.3
henry acceptable.

** For a power tranny to have a *primary resistance* of 2 ohms means it is
huge - 200VA size if 120 volt, 600 VA if 240 volt !! The secondary
winding is the one to go for then - something of about 30 VA and 20 volts
might be about 2 ohms.

However - you will have to pull all the laminations out and re-stack them so
the Is and the Es are together and create a small air gap. Something like
0.5 to 1mm would be in the ball park.

I don't like his chances of being able to pull apart a large mains E&I
trannie which has been well varnished, and thus
has well adhering lams.
0.5 to 1 mm gaps size might be right, but we are not told what
the purpose of the choke is to be.


By the time he does that without breaking the
bobbin or otherwise casusing damage, he could
have bought a Hammond choke.

But if the Hammond DCR is too high, then
he has to make something
Using a mains tranny will probably result in a very overweight
choke compared to what could be achieved with a new design.


To get 0.3H at 1A DC and 2 ohms would take a core about
50mm stack of 38mm tongue, and fill the bobbin with
1.4 mm dia wire. I am guessing, and a real design would have to be
worked out using Hanna's method, or following the
recipes in the choke ready reckoner tables.
It would be easier to make a new choke than stuff around
with a mains tranny.
I have a choke with the above dimensions, but its 2H at 0.5 amps,
and about 9 ohms.
To get 2 ohms, you need larger wire, fewer turns, so you get less inductance.


An old defunct tranny can be put into a log fire just to heat it to
dull red, and then removed, and allowed to cool down slowly.
This will vaporize the plastic bobbin, and the varnish,
and the whole item will fall apart easily when the bolts are undone,
and the wire cut off removed for recycling.
The magnetic properties of the core won't be altered since the slight annealing
won't hurt.
I measured some GOSS after firing, and it measured the same u
as before firing.

Its messy, sure, but I did a barrow load of old stuffed trannies last winter
in my open fire, and its saved me from having to purchases new stock.
I know where to get new plastic bobbins and winding wire.

I never re-use old winding wire from an old tranny.

Patrick Turner.





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

"Patrick Turner" wrote in message
...
: I measured some GOSS after firing, and it measured the same u
: as before firing.
:
: Its messy, sure, but I did a barrow load of old stuffed trannies last winter
: in my open fire, and its saved me from having to purchases new stock.
: I know where to get new plastic bobbins and winding wire.
:
: I never re-use old winding wire from an old tranny.

well, you could use it presumably to wind some series L to tame an SS amp
that has to drive a Quad ESL :-))

Rudy

: Patrick Turner.
:
:
:
:
:
: ........... Phil
:

I don't like his chances of being able to pull apart a large mains E&I
trannie which has been well varnished, and thus
has well adhering lams.
0.5 to 1 mm gaps size might be right, but we are not told what
the purpose of the choke is to be.


If the transformer is big enough, he could use it as is
before saturation sets in. Not efficient, and would never
be done in a commercial product, but if it's what he
has in the scrap pile... It would be twice (or is it
4 times) as big as a proper choke would be, but if the
transformer is "free" and he has enough room on the chassis,
it would work. It's somewhat similar to the use of a push
pull output transformer in a single ended amp. One would have to
set the quiescent current of the output tube at 1/2 the peak
current seen in the push pull amp to avoid saturation if you
don't modify the lams. You'd only get about 1/4 the audio power,
but it would work.

What about using an old flyback tranny out of a junk TV? Those are air
gapped, and can take pretty high current.

"gojamo" wrote in message
oups.com...
Since it's hard to find chokes, I was wondering if a power transformer
or audio transformer can be used for one. I need a couple with about
0.5 henry at least 1 amp. Thanks

tubesforall wrote:

What about using an old flyback tranny out of a junk TV? Those are air
gapped, and can take pretty high current.

Test one to find out.

To learn, you must build, observe, test, measure, measure again,
and again, note everything in a neat work book, and make
a conclusion as to whether the initial aim was fulfilled, and
list the reasons why succes was achieved, or list the reasons why
the selected item failed to fulfil the ambition you had for it.
This trains the brain to learn from experience,
and not all humans have this ablity........
I learnt the scientific method from my dad who was a vet,
and as a teenager I read his science class exercize books he prepared when
he was at school
some 35 years before me.
The method made sense to me, being a naturally observant person, and I did
well at Physics.
I failed all arty farty subjects like English, French and Latin, and I do
have to struggle
to say what I mean, and mean what i say, but I still hope I can inspire you
to
answer your questions by result of your own independant effort.
Would that not lead you to feel proud of yourself?
Years after I went through high school, and with no teachers to ask about
the
matters I investigated, I abandoned myself
into the shed I built for work and stayed there until I learnt about
triodes,
and a little practical electro magnetics, in the sole company
of some fine old books such as RDH4, where all your questions are better
answered
even though it will be in an indirect manner.



If you find yourself unable to comprehend Ohm's Law,
or impedance and resistance ideas,
and stare with a vacant mind free of questions while your equipmnent
you have hooked up produces only smoke, ask youself if you are really
able to be a technical person, or whether you'd be better off painting a
picture,
or being an accountant.

We hope you have some idea of basic safety procedures,
and that you are not prone to giving yourself a shock from
highish voltages every week.

A flyback tranny from a TV has some particular attributes.
What are they?


Patrick Turner.




"gojamo" wrote in message
oups.com...
Since it's hard to find chokes, I was wondering if a power transformer
or audio transformer can be used for one. I need a couple with about
0.5 henry at least 1 amp. Thanks

in article , tubesforall at
wrote on 4/11/05 11:38 PM:

What about using an old flyback tranny out of a junk TV? Those are air
gapped, and can take pretty high current.

"gojamo" wrote in message
oups.com...
Since it's hard to find chokes, I was wondering if a power transformer
or audio transformer can be used for one. I need a couple with about
0.5 henry at least 1 amp. Thanks



Offhand, I wouldn't think it would be suitable. But I AM sure it would make
an amplifier look like hell!

I think rearranging laminations would be your best bet. Maybe experiment
with an old doorbell transformer.

Jon

DoorBell trannies are for very intermittent use only. I wouldn't think it
would handle the current for long.

But another idea is to use a Japanese to US line matching transformer. The
resistance will be about right, and saturation should not be a problem with
the size of these babies. Available at surplus stores for a few bucks.

"Jon Yaeger" wrote in message
...
in article , tubesforall at
wrote on 4/11/05 11:38 PM:

What about using an old flyback tranny out of a junk TV? Those are air
gapped, and can take pretty high current.

"gojamo" wrote in message
oups.com...
Since it's hard to find chokes, I was wondering if a power transformer
or audio transformer can be used for one. I need a couple with about
0.5 henry at least 1 amp. Thanks



Offhand, I wouldn't think it would be suitable. But I AM sure it would
make
an amplifier look like hell!

I think rearranging laminations would be your best bet. Maybe experiment
with an old doorbell transformer.

Jon