Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old January 9th 19, 05:38 PM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

I see really expensive audio output and power transformers for sale
as well as cheap ones. And lots of folks really want older ones
because they are better than the new crop. So what is the difference?
It must be some sort of physical attribute. The way they are wound,
insulation, etc.
Is there a way to tell using just an oscilloscope? I'm just
curious. I am very happy with the way my tube amp sounds.
Thanks,
Eric

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Old January 10th 19, 08:13 AM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

wrote:
I see really expensive audio output and power transformers for sale
as well as cheap ones. And lots of folks really want older ones
because they are better than the new crop. So what is the difference?
It must be some sort of physical attribute. The way they are wound,
insulation, etc.
Is there a way to tell using just an oscilloscope? I'm just
curious. I am very happy with the way my tube amp sounds.
Thanks,
Eric


Frequency response delivering full power is what I think. Some trick
winding process is likely to cost more.

Greg
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Old January 10th 19, 02:09 PM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

Some things:

Quality of the core material.
Care and bulk of wiring.
Frequency range to be covered.
Power requirements.

After which, like anything else, all about materials wound on the thighs of virgins on Walpurgis Night.

Peter Wieck
Melrose Park, PA
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Old January 10th 19, 10:19 PM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

On Wednesday, January 9, 2019 at 9:32:20 AM UTC-8, wrote:
I see really expensive audio output and power transformers for sale
as well as cheap ones. And lots of folks really want older ones
because they are better than the new crop. So what is the difference?


The core of a transformer has laminations, because a solid metal lump
would have electrical conduction losses (eddy currents) to cause large
heat losses (and reduce output efficiency). A power transformer
has thick laminations (60 Hz losses are small anyhow, but at 60 kHz,
that would be inefficient), and a switchmode transformer is made of
high-electrical-resistivity ferrite (at 60 kHz, the size can be small, though
such a low-magnetization material wouldn't be great for lower
frequency power).

Audio transformers are most efficient when made from very thin laminations of
soft iron, which is a more expensive construction than is used for either
60 Hz or 60 kHz power transformers. It just has more small parts.


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Old January 11th 19, 05:14 PM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

On Thu, 10 Jan 2019 14:19:27 -0800 (PST), whit3rd
wrote:

On Wednesday, January 9, 2019 at 9:32:20 AM UTC-8, wrote:
I see really expensive audio output and power transformers for sale
as well as cheap ones. And lots of folks really want older ones
because they are better than the new crop. So what is the difference?


The core of a transformer has laminations, because a solid metal lump
would have electrical conduction losses (eddy currents) to cause large
heat losses (and reduce output efficiency). A power transformer
has thick laminations (60 Hz losses are small anyhow, but at 60 kHz,
that would be inefficient), and a switchmode transformer is made of
high-electrical-resistivity ferrite (at 60 kHz, the size can be small, though
such a low-magnetization material wouldn't be great for lower
frequency power).

Audio transformers are most efficient when made from very thin laminations of
soft iron, which is a more expensive construction than is used for either
60 Hz or 60 kHz power transformers. It just has more small parts.

Thanks for the edifying reply.
Some time back I wanted to use the mains power as a frequency standard
when adjusting a generator. I was worried about connecting my 'scope
directly to 125 volts so I used a 12 volt out step down xmfr. The
wave form was really distorted. So I guess this was a perfect example
of the xmfr being made in a way that was unsuitable for audio.
Thanks Again,
Eric
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Old January 11th 19, 11:07 PM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

On Friday, January 11, 2019 at 9:07:33 AM UTC-8, wrote:

Some time back I wanted to use the mains power as a frequency standard
when adjusting a generator. I was worried about connecting my 'scope
directly to 125 volts so I used a 12 volt out step down xmfr. The
wave form was really distorted.


That can happen because of saturation and remanence: the addition of a load on
the low voltage side (like, a light bulb) will help greatly. The best small-signal
audio transformers are potted in protective shells, in order to prevent
strain on the magnetic laminations (which makes the magnetic core
do those nonlinear things).
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Old January 11th 19, 11:34 PM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

wrote:



Audio transformers are most efficient when made from very thin laminations of
soft iron,



** Soft iron has not been used since the days of Michael Faraday.

Thin laminations of silicon steel is the norm.




Some time back I wanted to use the mains power as a frequency standard
when adjusting a generator. I was worried about connecting my 'scope
directly to 125 volts so I used a 12 volt out step down xmfr. The
wave form was really distorted.


** You exaggerate.



..... Phil
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Old January 11th 19, 11:36 PM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

whit3rd wrote:

The best small-signal
audio transformers are potted in protective shells, in order to prevent
strain on the magnetic laminations (which makes the magnetic core
do those nonlinear things).




** Where does this utter drivel come from ???


..... Phil


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