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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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12th May 2021, 6:59 pm | #1 |
Diode
Join Date: May 2021
Location: Appleton, Wisconsin, USA.
Posts: 5
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Speaker Dilemma
Good Afternoon.
I have a 1920's Amplion Model AR 114 speaker in which I believe the coil is open (zero ohms across the terminals). Personally, it is a unique and beautiful style that I've had for about 20+ years. The manufacturer did a remarkable job of assembling the driver case, for I have zero idea of how it was assembled or how to disassemble it. The driver case seems to be made of white metal or pot metal. That's just a guess. The back of the driver case has three "washer-like" objects at the 12, 4 and 8 o'clock positions that are flush with the case. There is no slot for a screw driver or anything to grip to remove. I have no idea of what purpose these three objects serve. The following pictures reveal the status thus far. Any recommendations as to disassembly of the driver case so the coil can be re-wound would be highly appreciated. Thank you in advance for suggestions. Additional pictures to follow. |
12th May 2021, 7:27 pm | #2 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,192
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Re: Speaker Dilemma
Hello and welcome to the forums.
Sorry to be a pedant, but zero ohms is a short-circuit rather that an open-circuit. The fact that some Digital Multimeters (DMM's) display a short circuit as something like 0L leads to constant confusion in the forums. Given that the speaker coil has a high impedance and resistance (2000R?) by design, it most likely is open-circuit, but I'd check before you open it up for rewinding.
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12th May 2021, 8:23 pm | #3 |
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Re: Speaker Dilemma
If the coil is open and you want it to work for demonstrations (they do sound pretty awful to us used to even the worst little radio) the coils could be rewound with a thicker wire and simply plugged into a MP3 player.
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12th May 2021, 8:28 pm | #4 | ||
Diode
Join Date: May 2021
Location: Appleton, Wisconsin, USA.
Posts: 5
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Re: Speaker Dilemma
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Any suggestions from the previous displayed pictures? |
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12th May 2021, 8:50 pm | #5 |
Octode
Join Date: Oct 2011
Location: Wrexham, North Wales, UK.
Posts: 1,457
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Re: Speaker Dilemma
I'm glad someone's mentioned the meter reading, the coil could be open but the OP has confused the terminology.
Coils don't usually short themselves out to the point of zero ohms, more likely to be infinity instead. Horn speakers will never be the best sounding thing in the world, they can't reproduce any low end and are designed primarily for speech.
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12th May 2021, 9:28 pm | #6 |
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Re: Speaker Dilemma
At a guess, the brass threaded section sticking out of the label side of the case is obviously a different material to the case and therefore must be a separate part. I think the knurled nut that was around it is what originally held the unit together, but now corrosion of the zinc alloy has got a grip. The screw down the middle of the brass part is the adjuster for the moving iron mechanism.
There may be corrosion grip where the two parts of the case meet around the periphery. A firm tap may be all that's needed, if my guess is right. However, the wire of the cois will go onto the terminals which are part of the case. Are there long fly leads, or do the terminals screw in far enough to mate up with the mechanism n the other part of the case? It's risky. Ideally someone's opened one before... David
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12th May 2021, 9:50 pm | #7 |
Heptode
Join Date: Jan 2006
Location: Cornwall, UK.
Posts: 501
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Re: Speaker Dilemma
If it's the same as the Amplion Dragon then precision drilling is involved; see page 13 of
https://www.bvws.org.uk/publications...letin_29_4.pdf |
13th May 2021, 12:24 am | #8 | ||
Diode
Join Date: May 2021
Location: Appleton, Wisconsin, USA.
Posts: 5
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Re: Speaker Dilemma
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13th May 2021, 2:45 pm | #9 |
Hexode
Join Date: Jun 2018
Location: Buckinghamshire, UK.
Posts: 382
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Re: Speaker Dilemma
This photo from the Radio Museum is of a different unit (AR35) but is of similar construction, and suggests three tapped holes in the main body:-
https://www.radiomuseum.org/forumdat...e%5Fein1%2Ejpg From page:- https://www.radiomuseum.org/r/amplio...horn_ar35.html It might seem the fixings have been designed to be tamperproof? Perhaps the marking on the 'screw heads' indicate a central driving peg has been cut off after placement? Cheers |
13th May 2021, 3:22 pm | #10 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Re: Speaker Dilemma
Could those three things in the photo be Mazak posts, formed in one half of the case, which have been riveted over? If so, these could be the cause of the need for precision drilling. Once the posts are drilled away, then some more drilling and tapping would allow the use of screws for reassembly.
It may be that the photographed unit was an earlier version with screws into tapped holes (that later got replaced/cheapened into rivet posts) OR it may be one which had posts, but was drilled out to be opened, and then drilled and tapped for reassembly. Just musing and guessing. David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
13th May 2021, 6:22 pm | #11 | ||
Diode
Join Date: May 2021
Location: Appleton, Wisconsin, USA.
Posts: 5
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Re: Speaker Dilemma
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Pictures to follow for future reference with others that may be contemplating the same procedure. |
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13th May 2021, 9:39 pm | #12 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: Speaker Dilemma
Might be worth sticking a hot soldering iron tip on the raised section just in case they have used a hard wax seal.
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13th May 2021, 11:42 pm | #13 |
Diode
Join Date: May 2021
Location: Appleton, Wisconsin, USA.
Posts: 5
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Another sincere Thank You to the forum members for steering me to the correct direction.
I have never seen that type of "screw". Instead of drilling out the "screws", a center punch was tried in a counter-clockwise direction, an lo and behold, they all backed right out. After sitting for 20+ years, the coils will now be sent out for a re-winding. Hopefully, someone else encountering the same dilemma will be helped by the pictures below. Pictures of the mystery fasteners. |