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T33 Ferrofluid - Anyone know?
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sydbar81
Junior Contributor 10+


Joined: 12 Apr 2018
Posts: 14
PostPosted: Tue Aug 07, 2018 9:30 pm    Post subject: Reply with quote
Another bump to an old thread.

I was able to confirm with Parts Express that their kits are APG-L14, which appears to be way off the mark:

Saturation Magnetization (Ms) 220 Gauss
Viscosity @27°C 2000 cP



I Spoke with Ferrotec and they suggested APG-O77N as a replacement for the AGP 512:

APG 512 (Magnetization: 300 Gauss, Viscosity: 75 cP) - discontinued

APG O77N (Magnetization: 265 Gauss, Viscosity: 115 cP)

APG S15N (Magnetization: 165 Gauss, Viscosity: 80 cP)


"Instead of APG S15N, we would suggest APG O77N. On the older speakers, the permanent magnets are weaker; therefore, we would recommend higher gauss ferrofluid. APG O77N has higher viscosity than APG 512, but as the coil/ferrofluid heat up, the viscosity is going to drop."
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speakerguru
Über Contributor 1000+


Joined: 18 Nov 2005
Posts: 1192
Location: Green Hut, Tovil
PostPosted: Wed Aug 08, 2018 9:23 am    Post subject: Reply with quote
sydbar81 wrote:

"On the older speakers, the permanent magnets are weaker; therefore, we would recommend higher gauss ferrofluid. "


Hmmm... If by older magnets they mean alnico then fair enough, but NT19s and NT25s were probably the first commercial tweeters to use the more powerful Neodymium magnets, which AFAIK have not been surpassed in strength.

I think the viscosity is the more important parameter for tweeters.
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