Edcor WSM Transformer Measurements

Hi there!

Last week I took delivery of basically one unit for each of the Edcor WSM: http://www.edcorusa.com/c/13/wsmseries range.
I bought a whole bunch to test with, and to try out in various projects I have on the go.

I'll be measuring all of them using a Peak Atlas LCR40 Pro: http://www.peakelec.co.uk/acatalog/jz_lcr40.html and recording the results in this thread (I did something similar for the Haufe RK173 here: http://groupdiy.com/index.php?topic=53286.0)
So you can flame me all you like for not using something more professional for measurement but it's all I have, so it's what I'll use.

More soon.

But I'll be as thorough as I can, since the Edcor site is rather light on this information across the range.

etheory said:

I'll be measuring all of them using a Peak Atlas LCR40 Pro
So you can flame me all you like for not using something more professional for measurement but it's all I have, so it's what I'll use.

Click to expand...

I won't flame you, but you may know that the measurement conditions on an LCR meter are very far from the nominal operation in an audio circuit. Typically, voltage and current in an LCR meter are an order of magnitude below intended operation, and the test frequency is much higher than the audio notion of low frequency. Most LCR meters do their measurements at 1k, some at 100Hz, but what we are really interested in is the behaviour at 20-50 Hz, where the saturation effects will be the more pronounced.
I always recommend using the voltage-divider method, i.e. putting a resistor in series, feeding it with a signal that is as close in amplitude and frequency as that it's going to be used, and measuring the voltage across the transformer winding.
Watching the waveform on a 'scope can be a real enlightenment, particularly with M6 core.

Here we go!

Edcor WSM transformers (all measured unloaded at 1KHz, no termination of other windings - this is just the individual windings by themselves):

2.4K:600R
1,2 primary first winding of C.T. - 1.001H, 45.8R
2,4 primary second winding of C.T. - 0.9948H, 51R
5,6 secondary first winding of C.T. - 294.9mH, 27R
6,8 secondary second winding of C.T. - 288mH, 24.1R

2.4K:10K
1,2 primary first winding of C.T. - 1.399H, 56.2R
2,4 primary second winding of C.T. - 1.385H, 68.2R
5,6 secondary first winding of C.T. - 4.665H, 152R
6,8 secondary second winding of C.T. - 4.621H, 127.3R

15K:15K
1,2 primary first winding of C.T. - 2.173H, 93.1R
2,4 primary second winding of C.T. - 2.148H, 107.4R
5,6 secondary first winding of C.T. - 2.122H, 114R
6,8 secondary second winding of C.T. - 2.116H, 100.9R

10K:10K
1,2 primary first winding of C.T. - 2.082H, 92.8R
2,4 primary second winding of C.T. - 2.058H, 106.8R
5,6 secondary first winding of C.T. - 2.050H, 116R
6,8 secondary second winding of C.T. - 2.046H, 100.6R

15K:600R
1,2 primary first winding of C.T. - 4.918H, 137.4R
2,4 primary second winding of C.T. - 4.867H, 160.9R
5,6 secondary first winding of C.T. - 276.5mH, 34R
6,8 secondary second winding of C.T. - 261.2mH, 29.8R

10K:600R
1,2 primary first winding of C.T. - 4.34H, 127R
2,4 primary second winding of C.T. - 4.282H, 147.2R
5,6 secondary first winding of C.T. - 348.1mH, 38.8R
6,8 secondary second winding of C.T. - 331.9mH, 33.7R

600R:600R
1,2 primary first winding of C.T. - 746.6mH, 29.6R
2,4 primary second winding of C.T. - 739.6mH, 34.8R
5,6 secondary first winding of C.T. - 731.1mH, 36.6R
6,8 secondary second winding of C.T. - 725.4mH, 32.4R

I understand that these testing conditions may or may not be vaguely useful, but it's all I have time for today.
If I get time for some more testing methods, I'll post them here also.

cheers

Well done. It is a pity the inductance measurements are made at 1KHz. The inductance of this type of core material varies a lot with frequency and from the design point of view it is most important at low frequencies. I am axpecting a couple of the 2K4:600 types in a few days time so I will check them out on my LCR bridge which can measure at 50Hz.

Cheers

Ian

ruffrecords said:

Well done. It is a pity the inductance measurements are made at 1KHz.

Click to expand...

Thanks! Unfortunately the LCR40 only uses 1kHz for testing when the inductance is high.
Is there a hand-held device that anyone knows of better suited to this type of testing?

For instance something that can connect to a computer and plot inductance and resistance over the audio range and then record this as a graph on the computer?
Even better if it's sub-1K dollars?

thanks!

(edit) - this looks like a great article on the topic: http://www.wikihow.com/Measure-Inductance

My transformers arrived in the post this morning. I had forgotten they are the XSM types (2.5 watts) not the WSM ones (0,5 watts)

I have an Agilent U1731C LCR bridge that I used to measure them. As these are bigger transformers there should be room for more wire and hence you might expect them to have a higher inductance. That said, they are about half the volume of the Carnhill VTB2291 types I normally use for 2K4:600 transforming and the bobbin seems to be les that half full of wire so.....

Here are the results I got measured at 100Hz and 1Khz


You can clearly see how the inductance rises at the lower frequency.

Cheers

Ian

if I have learned nothing else in 20 years of building studio mics it's that 1kHz means just about nothing to how a transformer behaves in real life.

For instance something that can connect to a computer and plot inductance and resistance over the audio range and then record this as a graph on the computer?
Even better if it's sub-1K dollars?

Click to expand...

http://mhsecure.com/metric_halo/products/software/spectrafoo.html

L measurments are handy but the thing they are predicting can be seen with the software program fully.  If I had budget in that range I'd get the sweeping software.  That way you can put it in a real circuit and get the final word in one go.  Plus you get lots of other useful testing programs with the package.

I measured about 42H @ 120Hz using handheld meter on the 2W 15K:600.  I attempted leakage L too but don't recall the figure.  For the circuits I've used Edcor 15K:600 in, my ears tell me extended top relative to bottom - in other words, not in balanced proportion.

I always recommend using the voltage-divider method, i.e. putting a resistor in series, feeding it with a signal that is as close in amplitude and frequency as that it's going to be used, and measuring the voltage across the transformer winding.

Click to expand...

Can we get a reliable figure from figuring out the resonant point with a cap?  I ask because the Edcor Matching series is not meant for DC so in tube circuits they would require a blocking cap, which will resonate with the priL at some point anyway.