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 Post subject: Magnavox Companion Speaker S-31 has continuity now- 17.5ohms
PostPosted: Nov Mon 18, 2019 2:33 am 
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The driver in my main console unit had two interestingly evaporated flex braid wires going to the cone. I repaired that with solder wick.

Now I cracked into the S-31 companion unit to order parts to rebuild the AMP150 inside and noticed the driver clicks with a 9V battery but the horn has no continuity at the terminals.

Not sure if I can get as lucky again with a DIY fix. Unsure the anatomy of the horn just yet. I'll crack into it tomorrow, but figured I'd give an ask here quick for dos/donts/maybes.

TIA!

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Last edited by radiopicker on Nov Tue 19, 2019 1:54 am, edited 1 time in total.

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 Post subject: Re: Magnavox Companion Speaker S-31 Horn has no continuity
PostPosted: Nov Mon 18, 2019 4:26 am 
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it is very common for these horns to be open or have risen in impedance/dcr due to a defective voice coil.

I've had many over the years that were defective upon arrival, both the deeper model horns and the more shallow horns with the green/blue magnet cover.

either the horn would be dead as a brick or it was whisper quiet.

these horns should scream midrange up to about 10-15k.

anymore, I have learned to count on them to be defective in a barn fresh set.

steve

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 Post subject: Re: Magnavox Companion Speaker S-31 Horn has no continuity
PostPosted: Nov Mon 18, 2019 11:51 am 
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Hi Steve,
Bummer. So are you able to handle it in any way? Do they break off near the terminals or deep inside the coil?
Wonder--if I can find the data for the horn (S-31 main unit) somewhere, or any knowledge of what materials and how to rewind the coil.
I'm not at all surprised then if this is how it is because I found it in not the driest of basements.

I'll try and tear down a bit when I get home this afternoon. Thanks for the heads up.

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 Post subject: Re: Magnavox Companion Speaker S-31 Horn has no continuity
PostPosted: Nov Mon 18, 2019 2:01 pm 
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i never wasted much time with them.

most of mine had a dcr anywhere between 2 and 40 ohms (defective). they are 16 ohm spkrs showing a dcr of 11-12 ohms when operating correctly.

they were a dime a dozen on ebay at one point, maybe they still are. i would buy from a reputable seller who can verify a replacement is good. put an ad in the classifieds too.

i never found a problem on the internal terminals. whether they were open or had an erratic dcr, the defect was inside the windings.

steve

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 Post subject: Re: Magnavox Companion Speaker S-31 Horn has no continuity
PostPosted: Nov Tue 19, 2019 1:45 am 
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a good horn is in the 9-12 ohm or so range? I have two 12" ones of the 1000cyl type by magnavox and they read about there. The 10"(?) one in this companion speaker was reading open as per this thread.

Tonight I cracked it open and couldn't find an immediate break, other than two I incurred myself taking the horn apart. :oops:

Here's where it gets interesting. Before I scrapped everything I unwound a couple turns. One side one way, and one side the other...to get the proper slack to make a repair and have a go.

Sure enough I have continuity now and a click with a 9V battery!

THE Bad news? Reading about 17.5 ohms, same meter as I get 10-12 ohms on "good" horns.


Thoughts on this? What might I expect from a) removing a couple turns b) an elevated resistance? audiowise speaking.

Thanks Steve! I'm not sure how common this one is, but it is model 580050. It seems the end cap housing varies from Maggie horn to another, but I wonder if I can grab a coil from another maggie horn of a 10 ohm dcr?

For now I'll have a go at 17.5ohms dcr and see what that sounds like.It'll be a week or so until I get the amp recapped.

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 Post subject: Re: Magnavox Companion Speaker S-31 has continuity now- 17.5
PostPosted: Nov Tue 19, 2019 3:28 am 
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see what happens, but i do know that when they go defective, the DCR can be all over the place.

also, they do not sound good at all when the DCR is off.

there are a couple versions of this horn. the large deep horn and the more shallow standard horns with the blue magnet cover.

i would get another horn that is verified to be good.

steve

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 Post subject: Re: Magnavox Companion Speaker S-31 has continuity now- 17.5
PostPosted: Nov Wed 20, 2019 1:44 pm 
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Those horns roll off mechanically around 13KHz if I recall correctly.

My suggestion is this.

If you want response up to 16KHz, find a modern horn lens of the same or close to the same size as the original then get a decent 16 ohm compression driver.


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 Post subject: Re: Magnavox Companion Speaker S-31 has continuity now- 17.5
PostPosted: Nov Thu 21, 2019 3:01 am 
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Thanks guys. I will rebuild the amp this weekend and have a listen. I unwinded a couple turns of wire from the voice coil, but I actually left the slack and spun it around the horn terminal for future reference if need be.

That being said a couple things still aren't clear to me, as this is new.

1) with a DCR of 17.5 ohms, what's causing this? All I do know is the horn was kept in a potentially damp basement. And that I unwound a couple turns (but repeat- did not eliminate length of wire).

A friend told me that DCR/impedance of voice coil are interrelated and that unwinding a couple winds could make the DCR increase, is this possible? Unfortunately I don't have a pre-unwound reading as the coil was reading open.

2) In terms of frequency response, does 17.5 ohms vs the "proper"10-12 ohms DCR make an audible difference to the human ear or would we have to be way higher DCR to notice?


I guess time will tell once I fire it up. So stay tuned. Thanks again

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 Post subject: Re: Magnavox Companion Speaker S-31 has continuity now- 17.5
PostPosted: Nov Thu 21, 2019 3:18 am 
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less turns = less DCR

i'm not sure what your friend is thinking.

unwinding a turn or so should not vary the dcr 4-5 ohms. even though you could not measure it due to it being open, i would tend to believe it was at 17 ohms before you unwound a turn.

i don't believe you will be happy with the sound/amplitude/etc. with it being off, especially if it is compared to a properly working horn.

these things should scream midrange with some HF too. i found out that any variation beyond 11-12 ohms DCR (16 ohms impedance) will definitely be noticeable when compared against a good horn.

to restore this set to the original state, toss ths horn and get one that is in good working order.

it will make a difference.

steve

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 Post subject: Re: Magnavox Companion Speaker S-31 has continuity now- 17.5
PostPosted: Nov Fri 22, 2019 11:51 am 
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Thanks!
Now why does the whole horn need to be trashed. Is there anything special about the coil other than 10-12 ohm dcr and perhaps the gauge of wire? Could I pop a coil in that is glued to a similar/same fitting diaphragm from a similar vintage "1000 cycle treble horn"

See this horn in the S-31 speaker is smaller than other mag horns I have here, maybe 10"? and I'd rather keep as much original as I can. i'm sure the horn itself and magnet are fine....But I could perhaps open up another 1000 cycle treble horn pul the coil and diaphragm its on and see if it fits in the high dcr horn?

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 Post subject: Re: Magnavox Companion Speaker S-31 has continuity now- 17.5
PostPosted: Nov Fri 22, 2019 12:59 pm 
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My suggestion would be to either find another horn or if the throat diameter and any mounting holes are a standard size you could perhaps find a compression driver to fit the horn.


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 Post subject: Re: Magnavox Companion Speaker S-31 has continuity now- 17.5
PostPosted: Nov Sat 23, 2019 6:18 am 
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radiopicker wrote:
Thanks!
Now why does the whole horn need to be trashed.


i won't waste my time with them, b/c they are a pain in the nose and replacements are easily found. they are plentiful on ebay and i would bet they can be easily found here in the classifieds as well, but since it is your horn, you can do whatever you like :) .

https://www.ebay.com/sch/i.html?_from=R ... n&_sacat=0

i have one of the top line extension speakers with the big magnet and bell cover on the woofer. this cabinet has the very large and deep heppner horn in it.

i crossed it over at 2K with a second order linkwitz. it sounds "fantastic vintage hifi" with PP tube amps.

steve

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 Post subject: Re: Magnavox Companion Speaker S-31 has continuity now- 17.5
PostPosted: Nov Sat 30, 2019 3:44 pm 
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What are you hoping to accomplish by unwinding turns from a voice coil? The exact dc resistance has little to do with it working or not.

Shorted turns, bad connections, and mechanical rubbing do. If there is a shorted turn you will likely not change that by unwinding a turn or two, but you may alter the frequency response or sensitivity or both depending on the number of turns removed

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