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In Reply to: RE: Can you explain why the 1kHz square wave being this shape posted by Eric Chan on July 02, 2024 at 03:43:57
Hi both,
The original photo showed my transformer supplier measuring the out put of the cutom made interstage and the output show overshoot and ringing in the falling edge, which is strange and I do not know the reason
I am doing an experiment here at home using lundahl interstage, as shown, the falling edge does not have any overshoot and ringing. I use also, well, the so called digital oscilloscope.
Is there something wrong with custom inyerstage or something else. The overshoot and ringing in rising edge are explainable, but how to interpret the overshoot of falling edge?
Follow Ups:
I don't think there's enough resolution to see what the falling edge is actually doing. How does it look at 10X that sweep?
Hi TK,
Does it look better
Pretty strange it happened in falling edge
I suppose because of the different level of deviation of the frequency response of the two DUT from ideal (gaussian response).
The device with the steepest out of band attenuation will exhibit the worst ringing and overshoot.
Omnes feriunt, ultima necat.
FWIW that's how the spark is generated for a spark plug in a car. You put a current through a transformer and then shut it off. When the field collapses, a spike is generated that is large enough to jump the gap of the spark plug.
I'm not used to seeing this in audio transformers though, even if the 'scope is digital. Usually you just get ringing on the leading edge. At any rate, the ringing can be reduced by loading the output of the transformer. I suspect that spike will go away to once the transformer has a load.
I have found this post
With a good ss amplifier you can test it in reverse mode.
Try to use Arta or Spectralab software with a good sound card 24bit / 192 kHz so you can see a lot of things.
The secondary acting as primary must be drive with a nominal Z as 8 ohm connected to ss amp
The primary acting as secondary must be closed with the nominal Rp of tube.
P.e. 700 ohm for 300B
In this way you can test the trafo for a great range of voltage; take a care on input sensitivy of audio card, ypu need round 40dB of attenuation.
not so complicated
And leave the simularion that are far for real world, it is fantasy
Walter
Edits: 07/14/24
But what do you expect when you do a reverse mode measurement? Shouldn't it be the same? Besides, most "good" ss amps don't go beyond 100kHz, so what's it worth?
With a good ss amp you can check a wide range of signals to get the max swing possible mainly in the bass region
You can't do this because it is impossible to have the right generator with the right Z
In a s.e. With 300B( example) to have 8 volt on 8 ohm you need almost 200 Vrms in the primary with Z of 700 ohm
Walter
There is nothing wrong to use a 300B to test a 300B transformer. And it is even better because you directly have the right bias and the right pre-magnetisation for the transformer.
For PP transformer it is better to use a variac (or on the primary or on the secondary). A ss can be broke if the transformer saturates.
The reason is to test the OT only without tube.
In the bass region ( where the Z tend to go lower for the limit of L ) and high region( parasitic) you see also the distortion of the tube and not how the OT works for a wide range of driving voltage.
And is not possible to get a high swing free of Thd to drive standard the trafo
It is a strong test for the entire stuff, iron + architecture
I have dozen of different test to show how OT respond at great signals; in the mid region normally it works perfect with low distorion.
I consider distortion measurements on (output)transformers not very usefull.
The distortion depends highly on the source output impedance for for low signals it also depends on the core material.
You don't get any valuable information the way you measure.
Hi
In attach some test on three different trafo with different power
Backward mode
Walter
There is no schematic how you measured it, any resistors?
In attach the basic set up
The ss amp drive the secondary acting primary through a resistor, in this case 6 ohm
On primary acting seconday there is a load with a partitor to check the signal
Walter
Edits: 07/16/24
I guess that you know that the resistor is part of the distortion measurements, in other words, changing the 6 Ohm resistor value will change the thd.
This is not an industry standard measurement so for me it is pretty useless.
Edits: 07/17/24
If it is not compliant with the industry is not a problem
I will check in this way
Even the R could be part of dist measurement it is linear and not non linear as tube
Your choice of the resistor value makes the current distortion a lot bigger.
The current is also in the transformer so not liniair.Read Radiotron designers handbook for the theory (or Partridge).
And yes it's a problem if you presents results on an open forum like this. At home you can do what you like, no one cares.
You should place a warning that the results are not very usable because of a different "standard" (and read also wrong* standard).* no bias = wrong for thd and power measurements. Even frequency response could be different but that depends on the design.
Edits: 07/17/24 07/17/24
If it is not compliant with the industry is not a problem
I will check in this way
Even the R could be part of dist measurement it is linear and not non linear as tube
The problem is that your method is wrong. What you present has nothing to do in a real tube amplifier with a real tube with a different impedance,
When i look at the frequency plots of the 3 transformers you posted earlier i think they all look horrible. I didn't even know that Sowter makes so bad transformers... Is it broke?
You didn't use a bias current, also a big mistake, and i mean a big big big mistake speacially when you try to measure thd with your method.
At last, if you post measuruments from brands like Sowter and Hammond, don't use the brand name only, post the exact type, both brands make a lot of different transformers. Is the thirth brand some local brand?
It seems that you are the same person banned 5 times in DIY forum
The method is always the same
And, as always, you haven't any fact to show us, only words.
I hope the administrator will read this post
Walter
Walter, your method is always the same, you present your methods as being the Truth, but without any scientific evidence. As with other topics on other forums, you simply ignore scientific articles by Patridge, one of the great legends in transformer technology, simply because you want to tell your own story. What a shame.
And now you're complaining about what? Because my knowledge is better than yours? Please don't be so childish.btw, you have to explaine the Sowter transformer too because Sowter has no information on there site which explains this kind of measurements. I think you are a liar.
Edits: 07/16/24 07/16/24
Don't worry
Be Happy
Walter
thank you Walter, the same for you. Please next time good arguments based on good and profen theory
Resistor 750 ohm added,mitigated, but falling edge still have overshoot
I seldom see falling edge having a overshoot
Can someone give a hint
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