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 Armature Speakers

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Join date : 2018-04-08

PostSubject: Armature Speakers   April 8th 2018, 8:03 am

I'm currently restoring a 1935 Zenith farm radio. This radio operates with a 6 volt battery. I have restoration almost compete, but am having an issue with the speaker. The sound is garbled, but pressing the armature down towards the cone clears up the issue. There is considerable force that keeps the armature up instead of centered in the coil assembly. I'm unable to disassemble the armature/coil assembly (mostly due to inexperience w/this style of speaker). I have 60+ years of experience with electronics including extensive vintage radio repair/restoration, but this is the first time I've run across a speaker of this type. BTW, I've designed and built a solid-state replacement for the inoperative 6-pin synchronous vibrator that fits in the original can... works like a charm. If anyone can help with this speaker issue, it would be much appreciated.
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Junior Member 50+ Posts
Junior Member 50+ Posts

Join date : 2017-04-09

PostSubject: Re: Armature Speakers   April 8th 2018, 8:48 am

The armature is probably hitting one or more of the four pole pieces. Look for a centering adjustment that bring the armature to the center. If there is no mechanical adjustment then there should be a solder blob that can be melted to re-position the armature.

There may be a rubber bushing involved, if there is and it is on the path of the sound vibrations and the bushing has hardened, a replacement bushing will have to be made.

What has to happen is that the all pole faces need to be free of rust and any other magnetic debris. That the armature is centered, and that there is no pre-load tension from the cone.

The speaker should be of the balanced armature type. If so speaker polarity is not important even if there is plate current flowing through the coils.

It is also possible the speaker has one or more critical mechanical components cast of pot-metal. The pot metal has expanded and warped. Pot metal degrades and expands with time, it also becomes very hard ceramic like. It cannot be drilled or cut without shattering, falling to crumbs. If the metal is a pot metal, grinding away to re-fit the piece may be the only option.


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