DC presence during operation is one thing and agreed from my part. But there is a claim, I highly regard as a myth, that running DC on such transformers permanently magnetizes the core and reduces effective flux density.
I don't think a typical DVM is going to have enough current to magnetize a core. Even if the core was magnetized you could always apply current in the opposite direction and reverse the process.
It´s not a myth...Look at what beyerdynamic says:
Also STUDER says this in the same manner in their servicemanuals for their consoles.
Here is the same:
Here you can find the entire documentation: https://www.audiomodellierer.de/VEB_Funkwerk_Kolleda.html
With voltage-matched input transformers, the current does not play a role because the power transmitted is very low and the transformer is mainly used for almost low-noise voltage gain. In this case, the change in voltage over the unit of time is crucial. This is also how induction is defined in this special context. DVMs use between 1.3 volts and 4 volts DC to determine resistance. Unfortunately, these are not myths. 🙂 Mr. Domsch describes this very well in his book. Best regards!
Also STUDER says this in the same manner in their servicemanuals for their consoles.
Here is the same:
Here you can find the entire documentation: https://www.audiomodellierer.de/VEB_Funkwerk_Kolleda.html
With voltage-matched input transformers, the current does not play a role because the power transmitted is very low and the transformer is mainly used for almost low-noise voltage gain. In this case, the change in voltage over the unit of time is crucial. This is also how induction is defined in this special context. DVMs use between 1.3 volts and 4 volts DC to determine resistance. Unfortunately, these are not myths. 🙂 Mr. Domsch describes this very well in his book. Best regards!
Yeah, avoid DC because the transformers aren't rated for DC and would saturate. Same thing happens to push pull transformers. But they won't be damaged by passing DC. Your meter outputs 4 volts but probably in the microamp range.
I do not and will not use DVM to determine the parameters. This is also not useful, since only the DC resistance is measured and not the impedance, which can vary significantly because it is very complex and also frequency-dependent.
Best regards!
Best regards!
In any case, it is not difficult to demagnetize an audio transformer. Hit it with enough AC current to saturate the core then back it off slowly.
There is a special procedure you will find at STUDER servicemanuals. It´s not a problem of AC currents...
Look how thin the individual wires of an input transformer are. If there is enough power, they tend to break down.
Current and voltage are completely different physical quantities.
Best regards!
Look how thin the individual wires of an input transformer are. If there is enough power, they tend to break down.
Current and voltage are completely different physical quantities.
Best regards!
This is from vital importance!
(Take care with ohm measurements expecially with low R ranges the current is higher and magnetization of core is much higher.)
....
Use only L meter.
First measure the Inductance of coils. with open ends one which are not measuring when measure the pair.
Inductance ratio is the same as impedance ratio and can be calculated. Also after deteminig prim and sec. You cam measure Lprim with shorted secondary to get Leakage inductance. Then calculate Mutual inductance and Coupling factor.
Capacitances also can be measured. That will not harm the transformer.
Still, not convincing why a transformer core should remain permanently magnetized, even after a high amount of DC applied. There is a reason they are called soft magnetics. Such phenomena would occur partially only near the hysteresis circumference. Which, especially for high-nickel cores should be much narrower than silicon steels. I cannot buy this claim, especially as detrimental factor to the transformer performance.
