KEF 107 T33 replacement?

[Dony]

Also, at some point I do want to replace the Ferrofluid in my T33's. I'm really just playing around with the SB to see what it sounds like and whether it might be an improvement. It would give us another option over the Morel, Audax, Vifa, MW sources.

This is a good thread on the Ferrofluid options at SpeakerTalk (SpeakerGuru is/was an original KEF engineer). Here's a link to FerroTec and for posterity this is some aspects of the thread;

• KEF used to use the now obsolete APG512. From memory it was a 75cp fluid. i.e. the fluid was used primarily to increase conduction of heat to the metalwork, not to provide damping. The base fluid is a synthetic oil and I guess everything dries/evaporates eventually.
• In the APG L series, APG L17would be the closest to the original low viscosity APG512.
  • APG311 looks closer still and has a higher temperature rating.
  • APG S15N looks to be close to the original in viscosity. If Ferrotec are cautiously recommending it, then it is probably the most suitable for T33 use.
• The exposed part of the T33 vc is high temperature cured epoxy, aluminium and CA (superglue) adhesive. Not much risk of a bad reaction with an oil based fluid, I think, but no guarantees.
• After some conversation with Ferrotec, it appears that due to the relative magnet strength the more critical parameter is the Gauss followed by viscosity. Therefore APGO77n is recommended as the best alternative with a gauss of 265/115cp.
  • Not sure what Ferrotec meant by that. There was never any explanation in their literature of what happens to the fluid if the field flux density is significantly greater or less than the quotes "Gauss"
  • When KEF tweeters first acquired ferrofluid, the primary aim was to reduce the thermal resistance of the air gap whilst introducing as little mechanical damping as possible. A viscosity of ~75cp does this.
• The magnet gap should "only just" be filled with ff. If 100ul (0.1ml) does not completely go right around the gap is does not matter. Do not overfill the gap. The vc length is less than the gap but takes up at least a third of the gap volume, so, if the gap is "only just" full, there will be sufficient coverage as the vc is inserted and displaces the ff.

Feel free to add any insight into this summary with your experiences.

Hi SimplySound,

With regards to replacing the ferrofluid in the T33, I've successfully replaced the ferrofluid in one of the T33 - SP1210 that came in my KEF 102. It is the same T33 model as what is installed in the KEF 107 from what I have researched.

With that said, I did accidentally damage the diaphragm in the second T33 from my KEF 102. Unfortunately there is no factory replacement diaphragm T33 available to purchase. So now I'm looking for a single spare T33 - SP1210 tweeter to purchase to have a complete pair of T33 as spares for my KEF 107. I now know that I will just need to be extremely careful with the diaphragm when I attempt to replace the ferrofluid.

Ultimately, what I wanted to mention is that there is a supplier in Canada that carries the current recommended Ferrotec ferrofluid for tweeters. The following is the link to that information.

Ferrotec's Recommendation for tweeters

Thanks

Don

Not sure if there is an equivalent vendor in the USA. I would imagine there is and it should only be a matter of locating the vendor to purchase the required fluid.

 

[SimplySound]

current recommended Ferrotec ferrofluid for tweeters

Careful there Dony, that link you supplied points to APG-L11(M). According to SpeakerGuru, at 200cp that would be too viscous. I belive going through the thread, the best recommendation would be what the Ferrofluid folks put forth, which is APG-S15N at 80cp. Not all ferrofluid is alike!

 

[Dony]

Careful there Dony, that link you supplied points to APG-L11(M). According to SpeakerGuru, at 200cp that would be too viscous. I belive going through the thread, the best recommendation would be what the Ferrofluid folks put forth, which is APG-S15N at 80cp. Not all ferrofluid is alike!

Hi Simplysound,

While I agree that the APG-L11(M) might not be the best for the T-33, the technician that is providing this information has indicated that he has replaced the ferrofluid in multiple sets of KEF T-33 with the APG-L11(M) fluid with great success.

The technician that is selling the Ferrotec ferrofluid in Canada has been working on speakers and electronics for decades, so therefore I will go with what he recommends as he has actually done the work and he is also in direct discussions/contact with Ferrotec for the recommendations that he has put forth.

My feeling is that should I need to replace my T-33 with the spare set then even if they last another 10 to 15 years with the new ferrofluid then I will be really happy as that will be an extension to the life of the tweeters compared to if I had not done the ferrofluid replacement at all. Plus it seems that the cost of other ferrofluid available from the US or internationally is much higher to us Canadians.

Thanks

Don

 

[DOBIEGUY]

Hey @Dony
Unless there is some issue with shipping ferrofluid to Canada from the US it’s available on Ebay from a major seller with free shipping.
Less than US$12 each. Buy two pre-measured 100ul tubes and you’re good.
Made by FerroTec.
Good luck

 

[Dony]

Hey @Dony
Unless there is some issue with shipping ferrofluid to Canada from the US it’s available on Ebay from a major seller with free shipping.
Less than US$12 each. Buy two pre-measured 100ul tubes and you’re good.
Made by FerroTec.View attachment 3087255
Good luck

Hi DobieGuy,

Thanks for the heads up. I think the question here is not whether ferrofluid is available or not. As mentioned I can get Ferrotec fluid here in Canada which saves on shipping and import taxes.

What is not clear is what is the correct type of Ferrofluid for the T33. The supplier in Canada recommends the APG-L11(M), Speakerguru recommends APG-S15N. I don't mind buying additional Ferrotec ferrofluid if required, but I just need to know what is the right specification.

Is the one shown on Ebay the APG-S15N specification or is it something else?

Thanks

Don

 

[DOBIEGUY]

Dony
Here is a photo from the FerroTec data sheet. I believe you’re over thinking this. The amount of fluid that you are installing is minuscule.
The fact that FerroTec packages this product in a few different sizes( for different diameter VCs) and prints the instructions with their name on it make it the product to use. I’ve done a few over the years with nothing but success.

 

[SimplySound]

Here is a photo from the FerroTec data sheet. I believe you’re over thinking this.

Just gonna say there are lots of options and you might not want to over think it... but you might also want to think it over. Higher viscosity will result in higher dampening. Does it matter to the responsiveness of the driver and quality of sound. Maybe, maybe not. If it sounds good, I wouldn't mess with it Dony, but if I were doing this fresh, I believe I'd use a fluid close to the spec... which is 75cp for the T33... per a guy that worked on them!

 

[DOBIEGUY]

I’d be interested to know where the ‘guy that worked on them‘ got the definitive, last word on what to use. Was it his opinion?
Use whatever you think is right.
I’m done here.

 

[Dony]

Dony
Here is a photo from the FerroTec data sheet. I believe you’re over thinking this. The amount of fluid that you are installing is minuscule.
The fact that FerroTec packages this product in a few different sizes( for different diameter VCs) and prints the instructions with their name on it make it the product to use. I’ve done a few over the years with nothing but success.
View attachment 3087328View attachment 3087329

Hi Dobieguy,

I think I am ok in using the Ferrotec APG-L11(M) as I don’t want to over think this.

However, with the new info. provided I have contacted the Ferrotec supplier in Canada to ask about the APG-S15N ferrofluid. If he advises that he is going to carry it or can order it in small quantities then I will probably order 100ul to have on hand to replace the ferrofluid in my original KEF 107- T33 when required.

In the end as long as I have one pair of T33 with fresh ferrofluid installed then all should be good.

 

[SimplySound]

I’d be interested to know where the ‘guy that worked on them‘ got the definitive, last word on what to use.

Ahhh... he worked on designing them, perhaps?

 

[Dony]

Well I heard back from the Ferrotec ferrofluid supplier here in Canada. The following is an excerpt from his email.

The particular fluid that I stock is a recommendation of Ferrotec Inc. itself as a general use fluid for 1” and 1.5” VCG tweeters, and as they are the supplier to many speaker manufacturers, I’d hope that they know what they are talking about…

Hands-on, I’d be surprised to learn that anyone would want to use anything thinner, as this stuff looks and feels like “really dark water”. When one brings the syringe (that I supply it in) near the voice coil gap, the ferrofluid is actually drawn out of the syringe without one having to depress the plunger. It’s a pretty neat sight to witness actually.

As I’m not a chemical engineer, I can only go with the manufacturers recommendation. I spoke with a fellow at KEF by the name of Chris (732)-683-2356 (extn.132) who had no reservations about me employing the Ferrotec fluid APG L11M for the T33’s

I think this is enough information for me, that and the fact that the technician has worked on a large number of tweeters over the years using the APG-L11M which indicates it should be fine. Also, without an easy way to source the Ferrotec APG-S15N ferrofluid it seems like it would simply be a lot of effort and maybe cost for no proven definitive benefit.

Thanks

Don

 

[bigbadhurbee]

Quick tip here about mounting the replacement MT1191 from Midwest Speakers to the KEF 107 tweeter faceplate.
I used Gorilla tape (made by gorilla glue) and it worked absolutely fantastic. Cut off a strip about 10” long, peel the backing off, and then apply right around the edge of the speaker. Trim the excess tape off right above the magnet. Squash the faceplate into the tape and hold for 60 seconds and your done!
Side note, I sanded the back of the face plate completely flat and roughed it up a bit for better adhesion.

 

[Dony]

Quick tip here about mounting the replacement MT1191 from Midwest Speakers to the KEF 107 tweeter faceplate.
I used Gorilla tape (made by gorilla glue) and it worked absolutely fantastic. Cut off a strip about 10” long, peel the backing off, and then apply right around the edge of the speaker. Trim the excess tape off right above the magnet. Squash the faceplate into the tape and hold for 60 seconds and your done!
Side note, I sanded the back of the face plate completely flat and roughed it up a bit for better adhesion.

Hi bigbadhurbee, thanks for the tip.

In my case I had custom faceplates made in a 3D printer that fit the new Audax tweeters and mount into the Kef 107. All the mounting screws fit perfectly and it looks almost original. The cost was $30 total.

 

[bigbadhurbee]

That’s awesome I didn’t know where to go to have that done myself plus I’m getting impatient to get this project wrapped up.
When I do the second speaker I’ll make a new post with some pictures and a quick how to again

 

[ernieS]

I have read a few forums that recommend using the Morel MDT29 tweeter as a replacement for the KEF 107. I have also recently seen a listing on Fleabay that claims to fix the original tweeter by replacing the Ferrofluid.

Here is a link to the Fleabay replacement:

http://www.ebay.com/itm/KEF-TWEETER...pt=Vintage_Electronics_R2&hash=item3a7c679bf8

Here is the link for the Ferrofluid replacement service:

http://www.ebay.com/itm/Repair-rebu...pt=Vintage_Electronics_R2&hash=item1e70819d50

Any suggestions would be greatly appreciated.
Thanks!

I’ve serviced many T33 and other uniQ models. The 107/2 tweeter was the most stress filled. I’ve never seen a used tweeter on the market. I’ve a few extra midrange.