Very special Allison CD-6s

[chewy]

Hi All,

After my introduction in the Welcome part of the forum I'd like to follow up with my next post...

These Allison's belonged to Colin Higham who was the founder of SEE Ltd. in Warrington who built the legendary revolver turntable. I suspect these have previewed many a prototype in their time and they almost met their end in a skip outside Colin's home. However I'm hoping to bring them back from the grave with a little (a lot) of TLC.

For the past 12 months after a house move the Allison's have been garaged and unfortunately got a little damp as a result, also one of the tweeters suffered damage during the move. Not to be defeated I've took on the task of reviving these little beauties and hope that Colin might get to listen to them once more.

I've seen the foaming kits on ebay but I've no idea just how easy or hard this is going to be. I suspect the challenge will be to get the old foam off, keep the cone central while I mount the new foam and keep the correct pressure around the mount whilst the glue goes off. Any advice would be most welcome...

Colin
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[struth]

Hi All,

After my introduction in the Welcome part of the forum I'd like to follow up with my next post...

These Allison's belonged to Colin Higham who was the founder of SEE Ltd. in Warrington who built the legendary revolver turntable. I suspect these have previewed many a prototype in their time and they almost met their end in a skip outside Colin's home. However I'm hoping to bring them back from the grave with a little (a lot) of TLC.

For the past 12 months after a house move the Allison's have been garaged and unfortunately got a little damp as a result, also one of the tweeters suffered damage during the move. Not to be defeated I've took on the task of reviving these little beauties and hope that Colin might get to listen to them once more.

I've seen the foaming kits on ebay but I've no idea just how easy or hard this is going to be. I suspect the challenge will be to get the old foam off, keep the cone central while I mount the new foam and keep the correct pressure around the mount whilst the glue goes off. Any advice would be most welcome...

Colin
143001430114302

Geoff(Walprgis) should be able to help you. he has done a lot of refoaming

[chewy]

Hi Struth,

Is that the correct spelling for Geoff (Walprgis)? Can't find him on the forum?

Kit ordered from here http://www.ekmpowershop25.com/ekmps/shops/speakerrepairs/fs8a-8-inch-refoam-kit-636-p.asp

Cheers
Chewy

[Marco]

Hi Colin,

Welcome to AoS, btw!

No, the daftee has missed out a 'u'. It's walpurgis :)

Marco.

[walpurgis]

I've been called worse! :)

[Marco]

Where does your username derive from anyway? If you've explained it before, I've missed it :)

Marco.

[walpurgis]

Where does your username derive from anyway? If you've explained it before, I've missed it :)

Marco.

Nowhere specific Marco. I've used variations of it elsewhere (as some know). It's just a word with some odd connotations that appealed :).

[The Barbarian]

I thought it was the German prog band of the same name at first..

1bpCgH12g14

[struth]

http://fc04.deviantart.net/fs71/i/2011/218/f/4/belphegor_walpurgis_wallpaper_by_panico747-d45oy3h.jpg

[trio leo]

I placed a set of photos re-foaming my Allison 3's on this forum, but I'm a computer numpty and I don't know how to direct you to the thread, I very carefully stripped the old foam and glue from the driver and surround, then I sliced open the driver dust cap to place shims between the piston and the shaft, but from what I can gather this is not necessary if you attach a battery to the driver to centralise it (out of my depth here).
re-foaming worked perfectly, as for the tweeter, it is a pulsating hemisphere and not pistonick like most tweeters, it moves like a jelly fish, I think with some tiny tools and a lot of patience they could be retrievable. good luck.

cheers Al

[Andrei]

Where does your username derive from anyway? If you've explained it before, I've missed it :)

He's a closet Mendelssohn lover.

http://i1279.photobucket.com/albums/y530/Andrei_nz/Walpurgis_zpss8vqo2yv.jpg (http://s1279.photobucket.com/user/Andrei_nz/media/Walpurgis_zpss8vqo2yv.jpg.html)

[chewy]

I placed a set of photos re-foaming my Allison 3's on this forum, but I'm a computer numpty and I don't know how to direct you to the thread, I very carefully stripped the old foam and glue from the driver and surround, then I sliced open the driver dust cap to place shims between the piston and the shaft, but from what I can gather this is not necessary if you attach a battery to the driver to centralise it (out of my depth here).
re-foaming worked perfectly, as for the tweeter, it is a pulsating hemisphere and not pistonick like most tweeters, it moves like a jelly fish, I think with some tiny tools and a lot of patience they could be retrievable. good luck.

cheers Al

Thanks Al,
Yep, used a little 9V battery from time to time to test speakers, basically sucks the cone in so I suspect if you leave it connected it will keep it in place. One point about the Allison's, the 8" sub points up which as you can see from the pictures means they're covered in dust the problem is this isn't just dust it's also years of grease and tar which means the dust has actually set! I'm using a stiff brush to get the majority of it off but at some point I'm going to need to get cleaner on it. White spirit will probably cut through but don't want to damage the cones, equally mild soapy water might work but again don't want to damage them.
How long did it take for the glue to go off on the surrounds?
Cheers
Chewy

[DSJR]

I remember the legendary Gilbert Briggs (who all but wrote much of the loudspeaker rule-book) saying that the best speakers he had were those used in the factory, for hours a day and covered in dust and grime. I really wouldn't worry about the Allison cones, as the dust may well add extra resonance damping without adding much if any mass as doping can and does I believe.

[walpurgis]

Here we go :).

You don't use a battery to centralise bass cones and you shouldn't need coil shims unless you've taken the cone completely out (unwise and probably damned awkward).

If the rear spider (the corrugated bit at the back of the cone inside the chassis) was OK and the cone was central before removing the front suspension/surround, you'd have to be pretty sloppy fitting the new surround to get the cone crooked enough for the coil to bind.

I do hope your new surrounds are of the exact correct dimensions and have the right profile.

Just get the cone edges and frame surround face as clean as possible. Usually scraping with a craft knife is adequate. Glue the new surround to the cone edges first, keeping it as near as the position of the original as possible. You should have the mark from the old glue to guide you. Once the glue is dry (if it's water based glue, leave it for a couple of hours). Locate the outer edge of the new surround loosely in its intended position. Use 'low tack' masking tape strips in three evenly spaced positions round the cone and out onto the outside of the front chassis edge. Not tight but just enough to hold the cone in position. Check for free back and forth movement. You may have to move the tape around a little. Once you are happy that the positioning is OK and that the cone moves freely and correctly, glue the surround with a small dab of adhesive to the frame at even spacings (between the tape strips) and allow to dry for about ten minutes (at ten minutes the glue will still be soft enough to detach the surround if there's a problem). Take the tapes off and check the cone still moves freely. If so, glue the rest carefully in place. I've found a smallish art brush best for applying the glue. You should be using water based adhesive.

An alternative to taping the cone is to use small blobs of BluTak under the outer edge of the surround in three positions to temporarily hold it in place prior to gluing. I've used both methods.

I believe said you'd cut the central dust cover dome on the cones (shame). If you can't get these looking presentable again, you should be able to locate replacements. Speak to me if you have trouble.

[chewy]

I do hope your new surrounds are of the exact correct dimensions and have the right profile.

Me too! Surrounds have arrived and they appear to be correct but a couple of observations, the outside circumference is perhaps a tad shy of the original and the angle of the inner ring doesn't match the angle of the cone. I expect that with the help of masking tape it would be held in place whilst the glue goes off but I don't want this to be a botch job. I would have thought that something like this would have carried technical specs such as outer/inner dimensions, angle, flex etc?

I can post pictures if it helps?

Cheers
Chewy

[walpurgis]

Pictures of the surrounds and cones would show the situation. Were the new surrounds specifically for this drive unit?

[walpurgis]

If you have the patience (there's quite a lot of it). Have a look through my old thread: http://theartofsound.net/forum/showthread.php?19555-My-new-(vintage)-Tannoy-Cheviots!

This shows how I replaced the surrounds on a pair of Tannoys. There is a difference, as the entire cone assemble was removed, but it has some pointers that may help.

[chewy]

14397144001440214404Very nice, puts my little Allison's to shame. Here are some pictures of the surrounds, taken outside on a very sunny day!

The first picture taken from above shows that the inner circumference matches the glue line pretty much, the second picture shows that the cone is sitting quite a bit lower than the rim and the new surround in profile indicates that the cone should be around level with the frame?

Cheers
Chewy

[walpurgis]

There is a fair bit of 'stretchiness' in foam surrounds and I usually work them a bit by stretching them about gently before use, just to get a bit more pliance out of them. Yours look as though they should be OK. I'd get them attached to the cone first and see how they sit against the chassis lip. You can stretch them into place if need be, but do ensure they stay concentric. The problem with surrounds that don't have a profile that matches the cone is that they can pull forward or backward once fitted, leaving the cone too extended or recessed. It's difficult to tell in advance how it will work out.

Surrounds can sometimes be persuaded to 'reset' themselves by holding the cone to just past the required position and using a hot (ish) hair dryer on them for a while and then letting them cool. (It's a dodge that can also be used to recentralise rear spiders)

[chewy]

I'm going to work on the basis that the spider needs to be level for the correct position, I suspect that there will be some stretch as you say once attached.

Wish me luck!

[walpurgis]

Fingers crossed! :goodluck:

[chewy]

So far so good...
Cones cleaned with a stiff brush and original foam removed
Metal cage rubbed down to remove loose paint and rust then wiped down with Kurust
Cone stabilised with polystyrene which also helped to lift the edge level with the cage
PVA glue applied to both faces and left for 10 mins to become tacky
Surround applied to cone with a little massaging to follow the original glue line

As the cones will sit slightly lower than the lip of the cage I'm wondering if I need to do anything more apply the glue to the outer edge, move the cone gently in and out to evenly distribute the glue then just leave it? The last picture shows the outer edge sitting pretty much flat and the cones are moving without rubbing...

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[walpurgis]

Keep going. It looks as though you are on the right track and I reckon it'll work out right :thumbsup:.

As the adhesive dries, gently squeeze the bonded surfaces together every now and then, as they may start separating a bit otherwise (I've had this happen).

[trio leo]

Allison drivers are coated with a thin tar like substance, I cleaned mine with a very slightly damp cloth and gently stroked the dust off 'til eventually they became clean without getting damp.
Once I had clamped the glued foam to the cage with pegs I left them to dry overnight. Once dry, I brushed a light coat of vinyl and rubber cleaner around the foam ring, it made them just a little more compliant and it helps to stop the foam drying out too much.

Good luck :)

cheers Al

[chewy]

Ladies and Gents I give you the revived Allison CD6s.

It seemed only fair that their first outing was a traditional track, so on went my copy of Dire Straits, "Telegraph Road", followed by a slightly more up to date Faithless "we come one" and finished with the breathy tones Joslin Stone and "Right to be Wrong" and I am more than a little impressed with the tone of these speakers. At first I was a little concerned that mid-ranges had been lost in the repair but once they warmed up and the foam I suspect became a little more pliant they took on a lot more depth. The only slight modification I've made to the original is the addition of washers to the screws to avoid tearing the foam when the screws were tightened.
It's not all great news however as I'm afraid the repair to the tweeter was not as I'd hoped. After reshaping the dome to as close to the original as possible I found that the structure was very weak and soft and unable to emit the higher frequencies. To give the dome some resilience I mixed a weak solution of water and pva and applied it to the dome, this imparted some strength and gave the tweeter legs, however I still feel it may have lost some of the frequencies in doing so. I am tempted to go back and try and manipulate the cone again but I'm afraid I may damage it this time around. All that said, the differences you have to be looking for and time will tell if it bothers me enough to revisit this again but for now I'm just enjoying them.

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Cheers
Chewy

[Gmanuk101]

wooah! cracking Job Colin Mate!!

[British high fidelity]

Fantastic retro fit, awesome

[Barry]

Where does your username derive from anyway? If you've explained it before, I've missed it :)

Marco.


This might help: http://en.wikipedia.org/wiki/Walpurgis_Night

[trio leo]

Well done Chewy,
As with all early Allisons they are meant to be no more than 3" from a wall, (room coupled) though with the 6's not near corners, I will ask my friend, I'm sure he told me of a company in Italy that specialises in repairing Allison drive units.

enjoy your music :)

cheers Al