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Old 23rd March 2013, 12:48 PM   #21
45 is offline 45  Italy
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Quote:
Originally Posted by Vinylsavor View Post
Hi!

I just wanted to express that I consider it bad style to relay such messages through another person, especially when it is critisism of a competitor. I know and like both Pieter and Per Lundahl and I respect them for their knowledge. I use the products of both of them in my designs.

I just pulled out my humble handheld LCR meter and measured the inductance of a LL1660/10mA. I get something like 25Hy for each primary which would be 100Hy when wired in series. I know that this meter is not very accurate for such measurements. In the past I did detailed inductance measurements using a signal gen and scope and running a frequency sweep across a resist and the inductance wired in series. Calculating the inductance from those measurements always gave higher values compared to that meter and typically closer to the spec of the transformer or choke under test.

As mentioned this also matches with the performance of these in actual amps. Would the inductance of the PP version really be only 23Hy, it would simply not work in many designs

Best regards

Thomas
If you could measure at 50 Hz it would certainly meet specs. LCR meters are meant for measuring chokes because these work at 100-120 Hz (i.e. rectified supply voltage) depending on the country. The LCR is also good for air core chokes as there is no core loss. No one cares about audio transformers too much as these represent a fraction near zero in the global market....you have to look for some expensive professional gear.
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Old 23rd March 2013, 12:54 PM   #22
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Hi 45 (nice nick by the way)

agree on this. My LCR measures at 100Hz

Best regards

Thomas
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Old 23rd March 2013, 07:53 PM   #23
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Quote:
Instead of relaying such strong critisism through a friend on a public forum Pieter should discuss his findings with Per Lundahl directly and then report the outcome. Both are professionals in transformer winding and should be able to sort that mismatch out.
Pieter Treurniet's reply:
Quote:
I don't agree.
Lundahl is responsible for their specifications; when they fall short this is a good place to notice because lots of DIY'ers depend on specifications for their designs. It is not my task to contact Per Lundahl.
An example of how it can (and should) be done: Hashimoto interstage transformer: 70H (Rated, Primary in Series; IB = 5 mA at 5V (50 Hz). I cannot compare Lundahls spec of just one number for inductance with specifications of other brands; when I measure 70 H instead of 290 H I am just curious how Lundahl arrive at their specification, that's all.
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Old 23rd March 2013, 09:19 PM   #24
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I am afraid but you friend is a bit wrong. The proof is in the Pimms website measurement for the LL1635/5mA which gives more than 16K at 20 Hz when loaded with 20K. So the inductance can only be close to 130H...
Pieter Treurniet's reply:

"45, I read that curve a bit different: at 20 Hz impedance is 10k6, that is effective inductance of 84 H; at 50 Hz impedance is 16k, that is effective inductance of 51 H; at 100 Hz impedance is 20k, that is effective inductance of 32 H. Nowhere near 130 H; maybe you need some (new) glasses?"

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Old 23rd March 2013, 09:29 PM   #25
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I think all those "experts" should know that you can't measure a SE transformer properly if you don't apply dc to it.
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Old 24th March 2013, 12:13 AM   #26
45 is offline 45  Italy
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Quote:
Originally Posted by Bas Horneman View Post
Pieter Treurniet's reply:

"45, I read that curve a bit different: at 20 Hz impedance is 10k6, that is effective inductance of 84 H; at 50 Hz impedance is 16k, that is effective inductance of 51 H; at 100 Hz impedance is 20k, that is effective inductance of 32 H. Nowhere near 130 H; maybe you need some (new) glasses?"

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Ha, ha, ha I don't need glasses. First that graph is not very representative as you get close to 100 Hz because you a have a resistor limiting the impedance. It can be somewhat useful only below 50Hz. Then maybe you should study some magnetism! Do you know how permeability works? It is only 1V applied. Have you ever heard about initial permeability? For that type of core with very small gap an increase of a factor of 2-3 is normal.
As a manufacturer you should know that there is quite a difference between minimum inductance and inductance. Minimum inductance is based on very small applied voltage and thus on initial permeability. I don't know any manufacturer which gives minimum inductance without specifying it. It would be like selling gold for brass!!
Rather than discrediting the others using your servant why don't you come here to discuss your transformers and show how good they are?

Last edited by 45; 24th March 2013 at 12:33 AM.
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Old 24th March 2013, 12:18 AM   #27
45 is offline 45  Italy
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Quote:
Originally Posted by esltransformer View Post
I think all those "experts" should know that you can't measure a SE transformer properly if you don't apply dc to it.
It is not exactly like that. You put a gap for a reason....
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Old 24th March 2013, 12:52 AM   #28
45 is offline 45  Italy
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Originally Posted by 45 View Post
First that graph is not very representative as you get close to 100 Hz because you a have a resistor limiting the impedance. It can be somewhat useful only below 50Hz.
Is is not even good enough at 50Hz because the reactance is too similar to the resistive load. In fact I put a real measurement of an OPT where it can be clearly seen that with open secondary it does have quite higher impedance at low frequency when the secondary is unloaded. Regardless of this reflected impedance drops inevitably even when the secondary load is such that the reflected primary impedance should be 3-4 times lower!

This is it again: 8K/6R PP transformer. Such transformer is rated for 270H minimum inductance (with 4V applied voltage) and 560H maximum inductance. Frequency is not specified.
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Last edited by 45; 24th March 2013 at 01:02 AM.
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Old 24th March 2013, 01:51 AM   #29
45 is offline 45  Italy
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Actually the frequency for which inductance is specified can be derived from the curve with unloaded secondary. It is 50Hz!
In fact the impedance with unloaded secondary at 50 Hz is about 85 Kohm which means that L=85000/2pi50=270H that matches precisely the specs (i.e 270 H for 4V input).
If I did the wrong math as Mr Pieter did, not accounting for the resistive load, I would get a lower value for sure even at 1Hz....

Last edited by 45; 24th March 2013 at 01:54 AM.
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Old 24th March 2013, 02:40 AM   #30
45 is offline 45  Italy
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Quote:
Originally Posted by Bas Horneman View Post
Pieter Treurniet's reply:
An example of how it can (and should) be done: Hashimoto interstage transformer: 70H (Rated, Primary in Series; IB = 5 mA at 5V (50 Hz). I cannot compare Lundahls spec of just one number for inductance with specifications of other brands; when I measure 70 H instead of 290 H I am just curious how Lundahl arrive at their specification, that's all.
If you measure the Hashimoto with 1V rather than 5V you won't be anywhere near 70H. I can bet on that. I think you need to measure inductances properly before saying that specs are not true. The inductance of a push-pull transformer is inevitably more affected by the input voltage because there is no (or very little in practice) gap. Does your LCR meter apply 5 Vrms signal? Mine doesn't...and on top of that you have to account for core losses as it measures at 120Hz.
If you load the LL1635/5 mA with a 20K resistor and you get almost 11K at 20Hz with just 1V applied it should be actually more than 130H. I would say something in the region of 170-180 H! At 50 Hz you will get 130 H at worst applying few more volts just like the Hashimoto.
1V rms applied to the IT in an amplifier like the one we are talking about here (i.e. a 6N7 driving the 45) means about 1 MILLIwatt output power and doesn't create any problem even if 130H is not the minimum inductance at 50 Hz with 1V input. 5V driving the 45 mean about 30 mW output power!
I gave for granted all this basic knowledge but it looks like this is not the case.

Last edited by 45; 24th March 2013 at 03:05 AM.
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