Antek Toroidal power transformer for Step-up, Measurements (part 1/2) - Page 3 - diyAudio
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Old 7th January 2012, 12:50 AM   #21
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Would using AC be a conclusive test for arcing as compared to low current high voltage DC?

I have been using these transformers exclusively for over a year now without fail. It is my opinion that the issue should be put in perspective. for me, I am using perforated steel ESL's at 3kv, while someone who has built wire ESL's need greater bias voltage. That construction method conversely would require an increases in power requirements and also increase the likelihood of arcing.
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Old 7th January 2012, 04:02 AM   #22
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Quote:
Originally Posted by dochungwell View Post
Would using AC be a conclusive test for arcing as compared to low current high voltage DC?
Yes. The AC test is appropriate since we are wanting to test for arcing inside the transformer due to voltage difference between the two 120V winding induced by the audio signal applied to the 6V windings. The DC bias voltage doesn't really come into play.

Quote:
I have been using these transformers exclusively for over a year now without fail. It is my opinion that the issue should be put in perspective. for me, I am using perforated steel ESL's at 3kv, while someone who has built wire ESL's need greater bias voltage. That construction method conversely would require an increases in power requirements and also increase the likelihood of arcing.
In post #15 you mention using an ADCOM 535II. Great amp, btw.
With 50V supply rails, at most you would be driving your transformers with 35Vrms.
This result in 650Vrms between the bifilar 120V windings.

Glad to hear you haven't had any issues in 1+ year of use...a good data point.
As you stated, if people require increased voltage drive the likelihood of arcing increases.
The hope is that the wire arcing test I proposed will give some qualitative data to help define how much voltage the transformers can safely handle.
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Old 7th January 2012, 01:00 PM   #23
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Excellence and quite useful qualitative data!

Another (non-topic) observation we have all noticed is that the ESL's drive with a lot less power from the amplifier than compared to my Magnaplanars, seemingly having a greater sensitivity....or is that because of the bias voltage acting as sort of a step-up pre-amp?

Regards,
Jerry/Doc
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Old 7th January 2012, 03:20 PM   #24
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This is because ESL's are voltage devices and have a higher impedance at lower frequency's,the opposite of a dynamic driver in which are current driven devices.

Therefore the only time an ESL starts to make any significant demand on the amplifier is at the higher frequency's most notably starting about 5khz to 10khz depending on the transformation ratio and the systems total capacitance.
Well above the critical information band of 300hz to 3khz.

At the lower frequency's because of this higher impedance most amplifiers can swing almost there full power supply voltage with very little current demand.
Making it almost effortless for them to be played at a high level of SPL's.

It is when the transformers core goes into saturation at low frequency's that create havoc on an amplifier.

Or when the resonate frequency of the transformer is lowered in to the audio passband because of a high leakage inductance with the systems total capacitance.
This is the reasoning for the adding of some resistance.

Both situations create a heavy current demand on the amplifier.
So,as Bolserst had mentioned the can be some trade offs in that area.
The ultimate goal is to not have to add any extra resistance at all, as you know resistance is just a waste of precious power. he,he,he
jer

Last edited by geraldfryjr; 7th January 2012 at 03:40 PM.
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Old 14th January 2012, 03:48 PM   #25
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Default Antek Transformer...secondary arcing test

I completed the arcing tests between the wires of the bifilar wound 120V windings.
The short answer is that:
- for amplifiers < 150W/8ohm, the two transformer setup should work fine without arcing
- for amplifiers > 150W/8ohm, I would recommend using a series/parallel combination of 4 transformers.


Attachment 1
Shows the preliminary arcing test setup with voltage applied between a twisted pair of the bifilar wound secondary wires.
The insulation withstood 1,000Vrms @ 1kHz for 5 minutes. But, I started noticing the distinct aroma of ozone.

Attachment 2
Turning out the lights, you could see corona forming around the wire pair at any voltage above about 600Vrms.
Pic shows corona for 750Vrms @ 800Hz. Corona only forms in air.
High voltage transformers use oil or resin impregnation to avoid this problem.

Attachment 3
Testing the whole secondary at 750Vrms, and the toroid gave a very pretty corona display. There is some resin or varnish applied to the secondary winding, but not enough to keep corona from forming. Sometime last night(after 2 days of constant 750Vrms) the insulation failed and arcing occured.

Over time, corona attacks the wire insulation and causes it to fail. It is a cumulative process. With this in mind, if I were to use these transformers for a hybrid ESL and planned to drive them with a 250W amplifier capable of 45-50Vrms output, I would use 4 of them instead of 2.

That being said, with the low peak/rms ratio of music it is highly possible that failure would not occur if only 2 transformers were used. But the possibility is there, and they are cheap enough that going from 2 to 4 isn't that painful to the pocket book. Also, with primaries in series-parallel, the core saturation capability is doubled allowing for lower crossover points if desired.

Alternatively, if your amplifier has good short circuit protection you could stick with the 2 transformer setup and just replace the set if you ever experience arcing.

Attachment 4
Here are two possible methods for wiring the primaries of 4 transformers in series-parallel.
I can't think of an advantage of one over the other...perhaps somebody else can.
.
.
.
Attached Images
File Type: jpg P1050456.jpg (137.0 KB, 373 views)
File Type: jpg P1050458.jpg (85.4 KB, 355 views)
File Type: jpg toroid_corona.jpg (23.2 KB, 356 views)
File Type: jpg Antek_4.jpg (107.0 KB, 368 views)
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Old 14th January 2012, 03:57 PM   #26
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Attachment4.
What is supposed to be different?
The impedance seen by the input voltage is identical for each arrangement.

Question:
If the corona is suppressed by potting, or whatever, does that change the reliability (no arcing) at high voltage operation?
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Old 14th January 2012, 04:09 PM   #27
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Quote:
Originally Posted by AndrewT View Post
Attachment4.
What is supposed to be different?
The impedance seen by the input voltage is identical for each arrangement.
There is no difference as far as input impedance or output voltage.
Only the arrangement of series-parallel connections of the 8 primaries.
One may be physically more convenient or simpler to wire up than the other, but electrically they will perform the same.

Quote:
Question:
If the corona is suppressed by potting, or whatever, does that change the reliability (no arcing) at high voltage operation?
Yes. If the transformer had been potted using a vacuum to ensure no air pockets remain, the corona would be suppressed and reliability would be improved.
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Old 14th January 2012, 04:38 PM   #28
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Excellent! Thanks for the information. Having recommended these Antek trannys to others based on nothing more than a listening test, I'm relieved to know their limitations. I drove a pair of them to stator-slapping volume [momentarily] with 225 watt/ch amps so I figured they were OK. At $13 each, even 8 of them for a speaker pair is a bargain, though, and they sound great too.

Last edited by CharlieM; 14th January 2012 at 04:44 PM.
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Old 14th January 2012, 05:37 PM   #29
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This is good to know.

I have a little more info that may go along with this,

Yesterday, I finally got a chance to fire up my little panels again with my newly rebuilt power supply.
I was able too have resealed the stators on both panels and they both will sustain a bias voltage of 10Kv with no apparent leakage or noises from the panels.

When I hooked up the transformer I would start to hear some slight noise ( hisses and crackkling) very faint at voltages above about 7.5kv.
But no major arcing was visible or heard.
Then the noise got slightly more noticeable at voltages above 8kv of bias voltage but ceased at lower voltage about 6Kv to 5.2Kv.
I suspect that this is caused in the transformers that I am using, and, are of similar construction.

I only got to listen to the panels for a short period of time because of a failure of one of the FET's in the power supply.

I will have this fixed shortly.

I'm not sure what had caused this as of yet as I have ran the thing very heavily without any issues so far.

But ,It was ramping up indicating a large current draw and drop in the output voltage that would level out at around 5.2kv.
This does seem to indicate a failure of the insulation of the transformer and was intermittent at different voltages above 6.8Kv until it broke down sustaining a corona discharge somewhere inside although I could not see it.

So I didn't get much farther on this and I hope to have more on it soon.

jer

Last edited by geraldfryjr; 14th January 2012 at 05:41 PM.
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Old 15th January 2012, 02:54 AM   #30
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Thanks for the in depth research Bolserst...this information will prove valuable as to the limitations of those transformers, as well as to the max amp output that should be utilized. My Adcom is a mere 65watts and does a fantastic job pushing these panels!

Jer, I found several of my panels experiencing similar noises issues, while I believed it was an issue related to the power supply, I soon learned in a failure analysis tear down it was a HV leakage from my front stator to the center charge ring terminal through the double sided tape.

Good luck!!!

Jerry/Doc
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