Field Coil Speaker

mavuser

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ive googled it and basically understand the difference between a field coil and PM speaker, but how do u know by looking at it, without taking it apart, if u have a feild coil speaker? should it have a power cord to plug into an outlet?
 

AcornHouse

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Usually a field coil speaker will have a small transformer (more than meets the eye) attached to the speaker basket, similar to an output transformer you'd find on a more modern amp chassis, but smaller.
sImg_4836.jpg
 

mavuser

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thank u gents! i suppose the tranny could possibly be mounted elsewhere in the speaker cabinet as well, if not right onto the speaker itself?
 

gilded

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That's true, Mav. It's also true that you'll see speaker frames into the '60s (or further?), that have a spot on the frame for a trannie.
 

adorshki

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OK this got my curiosity up, "Why use a field coil instead of a magnet, is there some advantage?"
So I did some digging and came across this thread:
http://antiqueradios.com/forums/viewtopic.php?t=158496
containing this post:
"I imagine they drive those field coils with well filtered and regulated DC, or else they are beyond nuts. One thing I've always noticed listening to field coil speakers used in the usual way (where the field coil doubles as a filter choke and there is a hum bucking winding on the voice coil), is that although the hum can be fairly low in the absence of sound, there is some kind of fairly nasty intermodulation distortion mixing 60 Hz or 120 Hz with the main audio. Very distinctive once you get to recognize it."
So thought Mavuser might want to know about that in case $$ are involved.
:friendly_wink:
 
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gilded

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I never heard anybody say there was an advantage to field coil speakers over magnets. I think when they started out, magnet technology wasn't so good, so field coil speakers were the available technology.
 

adorshki

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I never heard anybody say there was an advantage to field coil speakers over magnets. I think when they started out, magnet technology wasn't so good, so field coil speakers were the available technology.

Right, probably why the first ref that showed up was in a antique radio forum.
Was just kind of wondering "why even bother", unless it turned out they had some advantage, like maybe in very high output applications or something.
That thread I linked was pretty interesting and offered several reasons why different users might want them, but none of 'em seemed to be related to output.
Those guys sound just like us!
:friendly_wink:
 
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