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Yet another 105 recap question

 
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writethis
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Joined: 04 Sep 2014
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Location: Nashville USA

PostPosted: Fri Dec 13, 2019 10:20 pm    Post subject: Yet another 105 recap question Reply with quote

Still loving my first-series 105s. But after owning them for a couple of years now, they're sounding more dull and less punchy. So I finally decided to pull them out of my main system and take a look at the crossovers. When I opened up the woofer cabs, a couple of big electrolytic caps were literally hanging off their circuit boards by one lead. I'm not a recap fanatic, but this was all it took for me to commit to replacing all the 'lytics in one go. I plan to listen to these for the rest of my life, and imagine a fresh set of caps will last at least as long as I will.

This thread is about determining what values to replace with.

I do understand that these caps aren't supposed to match the listed schematic values. As it turns out, most of the caps on the speaker A crossover boards still match their counterparts on the speaker B crossovers quite closely. But all of them except one pair happen to be higher than listed spec. Is it remotely possible they've all drifted in the same direction to the same degree? Or am I safe to go with the measured values of the old caps when ordering replacements?

Representative examples:

C1 schematic: 80 actual measured: 92.52/89.59

C7 schematic: 100. actual measured: 129.9/130.1

C10 schematic: 3.3 actual measured: 4.33/4.30

Thanks in advance for any light you're able to shed.
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audiolabtower
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PostPosted: Sat Dec 14, 2019 2:48 pm    Post subject: Reply with quote

For what it's worth these were my values when I replaced the caps after about 8 years from new for polyester and polypropelene (not recommended without extra resistance to compensate for the elecs ESR).

C1 79.23/80.22

C7 95.66/95.37

C10 3.556/3.526

I have the original schematics somewhere, but they are almost completely faded now. The caps were sorted into 1 or 2% bands and used according to the driver measurements and measured inductor values. My C7s were obviously deliberately selected to be down from nominal and C10s to be up.

I would say yours have drifted too far and should be closer to nominal.

Does Falcon still do the replacement kits?
https://www.falconacoustics.co.uk/replacement-capacitor-sets/kef-1051-replacement-capacitor-set.html
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writethis
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PostPosted: Sun Dec 15, 2019 3:28 am    Post subject: Reply with quote

Thanks @audiolabtower. This is really helpful, I appreciate your willingness to share your expertise. Iíve bought KEF cap kits from Falcon, though itís been a few years now. Iíll reach out and see what they have. Cheers
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audiolabtower
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PostPosted: Sun Dec 15, 2019 2:12 pm    Post subject: Reply with quote

You're welcome. If they still have the 5% kits, that would be good, the most important thing is to keep the pair as close as possible. The most critical might be the tweeter caps, if one side is higher than the other, which you might see from the drift figures, then put the higher replacement values in the same place. Mine had 3.8uF on the tweeter side and 3.5uF on the amp side for example. Wrong way round the output will be higher and the hf impedance lower.
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writethis
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PostPosted: Mon Dec 16, 2019 7:35 pm    Post subject: Reply with quote

Again, thanks. One more fairly KEF-specific question: I assume the bitumen (?) that lines the cabinet interior was more supple or tar-like in consistency when new. Itís now brittle as can be. If one is truly attempting to restore a 40-year/old pair of 105 to their original state, does that include removing the old bitumen and replacing with Dynamat or something similar?
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audiolabtower
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PostPosted: Mon Dec 16, 2019 9:51 pm    Post subject: Reply with quote

I haven't bothered yet, mainly because can't hear any objectionable colouration, but it is an idea. Just be careful with any adhesives if they give off fumes and keep the B300s well away.
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writethis
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PostPosted: Tue Dec 17, 2019 4:17 am    Post subject: Reply with quote

You just helped me to feel okay about not prying that old stuff out. One has to draw the line somewhere, after all. Cheers
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speakerguru
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Joined: 18 Nov 2005
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Location: Green Hut, Tovil

PostPosted: Fri Dec 20, 2019 1:50 pm    Post subject: Reply with quote

writethis wrote:
Again, thanks. One more fairly KEF-specific question: I assume the bitumen (?) that lines the cabinet interior was more supple or tar-like in consistency when new. Itís now brittle as can be. If one is truly attempting to restore a 40-year/old pair of 105 to their original state, does that include removing the old bitumen and replacing with Dynamat or something similar?

It was always brittle in the cold, even when new. A knock test with a knuckle will tell you if the panel is damped or not.
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writethis
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PostPosted: Sat Dec 21, 2019 1:40 am    Post subject: Reply with quote

Thank you. Itís an honour to have you weigh in. The work youíve done over the years continues to bring me great joy.
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