Desmagnetizar un SET 845

No, se trata de etapas con válvulas en single ended. Un saludo!

Valvulator escribió:Con el cambio de polarización de los trafos de salida a las horas empecé a notarlo, llegado un momento el cambio fue espectacular, al tiempo me fui acostumbrando se estabilizó algo puede que también en mi cabeza. La mejora con el tiempo hizo que mereciera la pena.

 

Estás hablando del A.T.?.

Saludos.

No, esta operación se las hice a las Unison. Saludos!

Valvulator escribió:No, esta operación se las hice a las Unison. Saludos!

Lo que no entiendo, es que haya un cambio tan importante,............porque eres tu, sinó no lo hubiese creído. 

Saludos.

Resucitando un poco el tema.

Me encontrado en un librito-pdf de esos algo sobre el tema.Me ha pàrecido que podría ser interesante.


Saludos

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4.2 De-Magnetization

Some subtle problems are created when transformer cores and/or their shield cans become magnetized. Generally, cores become
magnetized by having dc flow in a winding, even for a fraction of a second. It can leave the core weakly magnetized. Steel cores,
because of their wider hysteresis loops, are generally the most prone to such magnetization. The only way to know if the core has
some permanent magnetization is to perform distortion measurements. A transformer with an un-magnetized core will exhibit
nearly pure third harmonic distortion, with virtually no even order harmonic distortion while magnetized ones will show
significant even order distortion, possibly with 2nd harmonic even exceeding 3rd. A test signal at a level about 30 or 40 dB below
rated maximum operating level at 20 or 30 Hz is typically the most revealing because it maximizes the contribution of hysteresis
distortion.

Microphone input transformers used with phantom power are exposed to this possibility whenever a microphone is connected or
disconnected from a powered input. However, distortion tests before and after exposure to the worst-case 7 mA current pulses
have shown that the effects are indeed subtle. Third harmonic distortion, which normally dominates transformer distortions, is
unaffected. Second harmonic, which normally is near the measurement threshold, is typically increased by about 20 dB but is still
some 15 dB lower than the third harmonic. Is it audible? Some say yes. But even this distortion disappears into the noise floor
above a few hundred Hz. In any case, it can be prevented by connecting and disconnecting microphones only when phantom
power is off. However, such magnetized transformers can be de-magnetized.

Demagnetizing of low level transformers can generally be done with any audio generator having a continuously variable output It
may take a booster of some sort to get enough level for output transformers (be sure there’s no dc offset at its output!). The idea is
to drive the transformer deeply into saturation (5% THD or more) and slowly bring the level down to zero. Saturation will, of
course, be easiest at a very low frequency. How much level it takes will depend on the transformer. If you’re lucky, the level
required may not be hazardous to the surrounding electronics and the de-magnetizing can be accomplished without disconnecting
the transformer. Start with the generator set to 20 Hz and its minimum output level, connect it to the transformer, then slowly (over
a period of a few seconds) increase the level into saturation — maintain it for a few seconds — then slowly turn it back down to
minimum. For the vast majority of transformers, this process will leave them in a demagnetized state.

Shield cans are usually magnetized by having a brief encounter with a strongly magnetized tool. Sometimes, transformers are
unknowingly mounted on a magnetized chassis. When the shield can of an input transformer becomes magnetized, the result is
microphonic behavior of the transformer. Even though quality input transformers are "potted" with a semi-rigid epoxy compound
to prevent breakage of very fine wires, tiny movements between core and can activate what is essentially a variable reluctance
microphone. In this case, a good strong tape head de-magnetizer can be used to de-magnetize the can. At the end of the production
line, most transformers are routinely demagnetized with a very strong de-magnetizer just prior to shipment. Although I haven't
tried it, I would expect that something like a degausser for 2" video tape (remember that!) would also de-magnetize even a large
steel-core output transformer.

"Audio Transformers"
by
Bill Whitlock

Jensen Transformers, Inc.

9304 Deering Avenue
Chatsworth, CA 91311

Valvulator escribió:Siempre me ha parecido molesto que no quede registrado el año en que se publican lo hilos y los comentarios en este foro, pero nunca he dicho nada... supongo que no seré el único.

Acabo de hacer miprimera "sugerencia"  

Sí que aparece la fecha en que se escribe el mensaje, fíjate, arriba primero viene en azul el título del mensaje y justo debajo en pequeñito lo primero tu nombre y después la fecha del mensaje

farancon escribió:

Valvulator escribió:Siempre me ha parecido molesto que no quede registrado el año en que se publican lo hilos y los comentarios en este foro, pero nunca he dicho nada... supongo que no seré el único.

Acabo de hacer miprimera "sugerencia"  

Sí que aparece la fecha en que se escribe el mensaje, fíjate, arriba primero viene en azul el título del mensaje y justo debajo en pequeñito lo primero tu nombre y después la fecha del mensaje

Perfil

Preferencias

Formato de Fecha.

Ya me pasó también 

Si, ya el año pasado cambie la configuración de fechas orientado por un amigo foreril y publiqué cómo hacerlo en el buzón de sugerencias ..

Salutti!!