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Latest restoration project, Thiel 04a

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I'm just in the planning stages of my next speaker resto project. So far I've restretched and reglued the parts of the grill that were peeling away. The woofers both need a refoam, but the sizing is really weird, anyone know a source for needed surrounds?

6" outer edge to outer edge for surround

4.25" outer edge to outer edge for cone

Anyone know if the tweeters need ferrofluid, or any info on recapping the crossover? I've heard Thiels have overly complex crossovers.


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  • 1 month later...

I finished restoring these a couple of weeks ago, and have been listening to them everyday since. They really are a superb speaker, and I encourage anyone who finds a pair to put in the work to get working. The sound signature is on the bright side of neutral. The highs are really detailed, yet there's little if any siblance. The bass is there, but it's on the polite side, and is actually quite impressive considering they're produced by what amounts to a 6" woofer. Anyway, I figured I'd document this to help out anyone who finds a pair. 

I'll start with the woofers. Don't try to find surrounds from your usual sources. Odds are they won't fit, actual size is in between a 6" and 6.5". This here was a perfect fit. https://www.midwestspeakerrepair.com/shop/speaker-repair-kits/6-5-inch-refoam-kit-f6-1/


Both of my tweeters were dead too. I tried unwinding one coil so that there'd be enough wire to reconnect. Doing so dropped the impedance really low. They were supposed to be 8ohm, but after unwinding I got 2.8ohms in one tweeter, and 1.6ohm (both ends needed to be unwould and extended in this on) in the other. The tweeters are labeled "Polydax" and had a faded model number that I think is "HD130xi34".


Through research it seems "Polydax"and "Audax" are one and the same, so I was able to find what seemed like a similar tweeter, the "Audax HD13d34". Which through more research I've found they have a modern version that was supposed to be "Improved", the "TW034X0". Diaphragms and voice coils only for the TW034X0 are available from Madisound. I initially purchased these. DON'T USE THESE, THEY WILL CAUSE MIDRANGE DISTORTION!  Looking at the specs, the TW034X0 and HD13d34 are identical for resonant frequency (TWO34xo = 800Hz, HD13d34 = 900Hz). I tracked down a pair of HD13d34 on ebay, seller said they came out of a pair of "Phase model D".

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Upon receiving the HD13d34, it was immediately obvious it couldn't just be dropped intho the Thiels. The magnet was significantly larger. I then went on to carefully transfer the diaphragm and voice coils over the original magnets, which went without a hitch. Both tweeters measured 6.8ohm when complete. 

Finally I turned my attention to the crossover. Far as I can see, all the caps are =/-20% tolerance. There were only w electrolytic caps on each crossover, so I opted to only replace those. They are 50uf 100v, and 4.7uf 50v. I used PE Dayton 5% caps as replacements. The crossover is a lot of work to remove, so I opted to do the work with the crossover still inside the speaker. There was just enough room, if you pushed the wires aside, to snip the original cap legs, twist the replacement legs with what was left inside, and solder them together. 


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