UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 12th May 2021, 6:59 pm   #1
DrAtwood
Diode
 
Join Date: May 2021
Location: Appleton, Wisconsin, USA.
Posts: 5
Default 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.
Attached Thumbnails
Click image for larger version

Name:	P1030008RepRed.jpg
Views:	164
Size:	50.2 KB
ID:	233882   Click image for larger version

Name:	P1030012RedRep.jpg
Views:	170
Size:	124.9 KB
ID:	233883   Click image for larger version

Name:	P1030013RedRep.jpg
Views:	158
Size:	144.1 KB
ID:	233884   Click image for larger version

Name:	P1030015RedRep.jpg
Views:	167
Size:	89.4 KB
ID:	233885   Click image for larger version

Name:	P1030011RedRep.jpg
Views:	145
Size:	115.1 KB
ID:	233886  

DrAtwood is offline  
Old 12th May 2021, 7:27 pm   #2
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,192
Default 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.
__________________
Graham. Forum Moderator

Reach for your meter before you reach for your soldering iron.
Station X is online now  
Old 12th May 2021, 8:23 pm   #3
Guest
Guest
 
Posts: n/a
Default 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.
 
Old 12th May 2021, 8:28 pm   #4
DrAtwood
Diode
 
Join Date: May 2021
Location: Appleton, Wisconsin, USA.
Posts: 5
Default Re: Speaker Dilemma

Quote:
Originally Posted by Station X View Post
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.
Thank you. I should of said that my meter showed no numeric resistance. I presuming an open coil.

Quote:
Originally Posted by merlinmaxwell View Post
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.
Thank you. That is a goal to have the coil rewound. But for the life of me, I do not know how to open the driver case.

Any suggestions from the previous displayed pictures?
DrAtwood is offline  
Old 12th May 2021, 8:50 pm   #5
Glowing Bits!
Octode
 
Glowing Bits!'s Avatar
 
Join Date: Oct 2011
Location: Wrexham, North Wales, UK.
Posts: 1,457
Default 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.
__________________
Rick, the annoying object roaming the forum.
Glowing Bits! is offline  
Old 12th May 2021, 9:28 pm   #6
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
Default 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
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Old 12th May 2021, 9:50 pm   #7
Simon Gittins
Heptode
 
Join Date: Jan 2006
Location: Cornwall, UK.
Posts: 501
Default 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
Simon Gittins is offline  
Old 13th May 2021, 12:24 am   #8
DrAtwood
Diode
 
Join Date: May 2021
Location: Appleton, Wisconsin, USA.
Posts: 5
Default Re: Speaker Dilemma

Quote:
Originally Posted by Radio Wrangler View Post
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 coils 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 in the other part of the case?

It's risky. Ideally someone's opened one before...
David
Thanks David for the suggestion. The fly leads appear internally long.

Quote:
Originally Posted by Simon Gittins View Post
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
Thanks Simon. A very interesting read giving some insight. My Amplion AR 114 drive case is somewhat different in assembly than the Amplion Dragon, with three objects located at the 12, 4 and 8 o'clock position on the back of the driver case with no way of removing them. The back of the driver case is pictured below showing a close up of their appearance. I'm somewhat suspicious of them being involved with securing the case together. Any further information of what they are is appreciated.
Attached Thumbnails
Click image for larger version

Name:	P1030011RedRep.jpg
Views:	75
Size:	115.1 KB
ID:	233903   Click image for larger version

Name:	P1030016RedRep1.jpg
Views:	82
Size:	94.0 KB
ID:	233904   Click image for larger version

Name:	P1030016RedRep.jpg
Views:	81
Size:	67.6 KB
ID:	233905  
DrAtwood is offline  
Old 13th May 2021, 2:45 pm   #9
Trigon.
Hexode
 
Trigon.'s Avatar
 
Join Date: Jun 2018
Location: Buckinghamshire, UK.
Posts: 382
Default 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:-

Click image for larger version

Name:	Amplion AR35 Schalldose_ein1.jpg.jpg
Views:	97
Size:	37.1 KB
ID:	233932
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
Trigon. is offline  
Old 13th May 2021, 3:22 pm   #10
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
Default 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
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Old 13th May 2021, 6:22 pm   #11
DrAtwood
Diode
 
Join Date: May 2021
Location: Appleton, Wisconsin, USA.
Posts: 5
Default Re: Speaker Dilemma

Quote:
Originally Posted by Trigon. View Post
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:-

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
Quote:
Originally Posted by Radio Wrangler View Post
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
Gentlemen. A sincere Thank You for these suggestions. I believe you've both identified the assembly process that potentially was designed to be tamper proof. I shall attempt disassembly via precision drilling and then re-tap for assembly.

Pictures to follow for future reference with others that may be contemplating the same procedure.
DrAtwood is offline  
Old 13th May 2021, 9:39 pm   #12
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
Default 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.
PJL is offline  
Old 13th May 2021, 11:42 pm   #13
DrAtwood
Diode
 
Join Date: May 2021
Location: Appleton, Wisconsin, USA.
Posts: 5
Default

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.
Attached Thumbnails
Click image for larger version

Name:	P1030016RedRep1.jpg
Views:	64
Size:	94.0 KB
ID:	234011   Click image for larger version

Name:	P1030017RedRep.jpg
Views:	63
Size:	69.4 KB
ID:	234012   Click image for larger version

Name:	P1030022RedRep.jpg
Views:	67
Size:	96.6 KB
ID:	234013  
DrAtwood is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 12:56 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.