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Old 4th February 2014, 09:30 PM   #1
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Default transformer test

I found some nice transformer tests and i was wandering what my own transformer would do in a similar test.

First the site where you can read some tests:
SAC Thailand
http://diyhifisupply.com/files/silks325.pdf

I did my test with a real tube, EL34 in triode mode 80mA. (sorry the real 300B was not available and for this test there will be minor differences)

The transformer is a single ended double HiB c-core 3500 Ohm / 8 Ohm 60mA-120mA 30W at 18Hz. Copperloss 0,14dB.

I noticed that the best SE transformer have the most problems at low frequencies (core saturation or to low inductance)

Did anybody do similar tests?

frequency response
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squarewaves
1kHz
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10kHz
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20kHz
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100Hz
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40Hz
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Last edited by esltransformer; 4th February 2014 at 09:52 PM.
 
Old 4th February 2014, 10:11 PM   #2
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Quote:
Originally Posted by esltransformer View Post
I found some nice transformer tests and i was wandering what my own transformer would do in a similar test.

First the site where you can read some tests:
SAC Thailand
http://diyhifisupply.com/files/silks325.pdf

I did my test with a real tube, EL34 in triode mode 80mA. (sorry the real 300B was not available and for this test there will be minor differences)

The transformer is a single ended double HiB c-core 3500 Ohm / 8 Ohm 60mA-120mA 30W at 18Hz. Copperloss 0,14dB.

I noticed that the best SE transformer have the most problems at low frequencies (core saturation or to low inductance)

Did anybody do similar tests?
Can you list your test equipment and testing procedure? I'd like to test a few transformers, but don't know where to start. Thanks.
 
Old 4th February 2014, 10:44 PM   #3
45 is offline 45  Italy
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I do.
I am not sure about your numbers. Even without considering that pretty small loss, what is the Bmax (AC + DC) you get for 30W at 18Hz with 120 mA DC current and 30H minimum (i.e. with 10 Gauss AC)? Although the C core has an advantage respect to E+I in terms of size for the same specs the difference is not like between night and day.
The biggest core I consider acceptable is the EI 150/70 (i.e. 50x70 core size) and this would not be enough! 50x75 would be the minimum to achieve 30W at 18Hz with 120 mA DC current at my usual Bmax = 7500 G. So I would need to accept higher B at that frequency for 30W (and thus more distortion because in less linear area). A 50x70 core alone weights about 8.5Kg!!! For a reasonably sized transformer those numbers are impossible. Specifying max power at 30Hz is more than enough for SE OT, provided that will work not so close to saturation (7500 Gauss total induction limit for E+I and a bit higher for C cores). Together with an inductance that gives a ratio between reactance at 30Hz (i.e. 2*pi*f*L) and equivalent resistance (i.e. the plate resistance in parallel to the nominal primary load) equal to 8 it will already guarantee low distortion at least down to 30Hz. Of course the higher the better but practicality cannot be ignored at some point..... what's the point of having a huge transformer to get those numbers down to 20Hz rather than 30?
 
Old 5th February 2014, 07:11 AM   #4
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Maybe i did better write at 120mA 18Hz 30W the transformer will just saturated (2,01T (ac + dc))

It was not specially made to "handle 30W", just for 300B and her sisters (so more up to 20W )

EI is far more less linear and can handle less power.

I did not wanted the standard 300B transformer what have saturation at 10W-13W 15-20Hz.



Quote:
Originally Posted by 45 View Post
I do.
I am not sure about your numbers. Even without considering that pretty small loss, what is the Bmax (AC + DC) you get for 30W at 18Hz with 120 mA DC current and 30H minimum (i.e. with 10 Gauss AC)? Although the C core has an advantage respect to E+I in terms of size for the same specs the difference is not like between night and day.
The biggest core I consider acceptable is the EI 150/70 (i.e. 50x70 core size) and this would not be enough! 50x75 would be the minimum to achieve 30W at 18Hz with 120 mA DC current at my usual Bmax = 7500 G. So I would need to accept higher B at that frequency for 30W (and thus more distortion because in less linear area). A 50x70 core alone weights about 8.5Kg!!! For a reasonably sized transformer those numbers are impossible. Specifying max power at 30Hz is more than enough for SE OT, provided that will work not so close to saturation (7500 Gauss total induction limit for E+I and a bit higher for C cores). Together with an inductance that gives a ratio between reactance at 30Hz (i.e. 2*pi*f*L) and equivalent resistance (i.e. the plate resistance in parallel to the nominal primary load) equal to 8 it will already guarantee low distortion at least down to 30Hz. Of course the higher the better but practicality cannot be ignored at some point..... what's the point of having a huge transformer to get those numbers down to 20Hz rather than 30?
 
Old 5th February 2014, 07:12 AM   #5
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You can look at the link i already gave. This test set-up can be used, brand of test equipment is less important.


Quote:
Originally Posted by sporc View Post
Can you list your test equipment and testing procedure? I'd like to test a few transformers, but don't know where to start. Thanks.
 
Old 5th February 2014, 09:14 AM   #6
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Here some datasheet from one of the best transformers i could find:
Tango FC-30-3.5S, this is the bigger brother of the Tango XE 20S

I don't know exactly what Tango mean by 30W (40Hz) is this core saturation? My guess is yes. So still a bit weak in the low frequency range.

Click the image to open in full size.
 
Old 5th February 2014, 09:36 AM   #7
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There is no test voltage for the primary inductance measurements, or technique for the leakage inductance - which is a bit of a pity.
 
Old 5th February 2014, 09:42 AM   #8
45 is offline 45  Italy
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Quote:
Originally Posted by esltransformer View Post
Here some datasheet from one of the best transformers i could find:
Tango FC-30-3.5S, this is the bigger brother of the Tango XE 20S

I don't know exactly what Tango mean by 30W (40Hz) is this core saturation? My guess is yes. So still a bit weak in the low frequency range.

Click the image to open in full size.
Not so much, it is good in most cases. It means just below saturation. If you back it a bit it is still very good down to 30Hz for most 300B amps that don't do more than 10W. Often they only manage 8W.
esltransformer there is nothing you can teach Japanese about audio transformers....
 
Old 5th February 2014, 09:45 AM   #9
45 is offline 45  Italy
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Quote:
Originally Posted by trobbins View Post
There is no test voltage for the primary inductance measurements, or technique for the leakage inductance - which is a bit of a pity.
Japanese brands usually do it the right way (i.e. 4-5V signal applied to the primary for inductance, for example) at 50Hz.
 
Old 5th February 2014, 09:52 AM   #10
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Quote:
Originally Posted by 45 View Post
Not so much, it is good in most cases. It means just below saturation. If you back it a bit it is still very good down to 30Hz for most 300B amps that don't do more than 10W. Often they only manage 8W.
esltransformer there is nothing you can teach Japanese about audio transformers....
Of course not, but they have weaker bass, higher loss and very high prices. (but very nice finish ) All thinks i not like so much.
I think they are able to make "a better" transformer if they wanted to but they do not.....

Last edited by esltransformer; 5th February 2014 at 09:54 AM.
 

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