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Franken-Kef 105 1/2 refurb project

 
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essem
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Joined: 27 May 2016
Posts: 3
Location: Melbourne, AU

PostPosted: Sun Dec 04, 2016 8:25 am    Post subject: Franken-Kef 105 1/2 refurb project Reply with quote

Greetings from Melbourne Australia.

First, may I say thankyou to all who contribute here sharing so much information about these wonderful vintage speakers and your experiences with them. A while back I acquired a very unusual pair of original 105's: the bass unit and crossovers of the original Mk I but with the head unit from a Mk II. This means the crossover is external by necessity. There's not alot of wire to play with and the crossovers just hang about at the back of the heads; pretty darned ugly.

You can see a few pictures of them here:
http://rdxx.org/kef/kef105/img/

The protection circuitry has been removed and bypassed, which I am ok with. There's signs of burnout on one of the woofer crossovers. That's a bit of a worry. Other than a replaced C1 on the SP1060, the crossovers look original. I have some new 2% Alcaps from Falcon on their way to me, and I'm also asking them about possible replacements for the burnt bits.

Given this rather odd state they are in, with thin solid core wiring (about .8mm diameter, 20awg? perhaps ok?) and massive solder globs on their terminals, they already sound quite wonderful, so organic and musical and very revealing of what's upstream. We just had a big hifi show in Melbourne. These old babies hold their own for sure. Definite long term keepers. I am in love with my crazy franken-Kef Dalek's!

I'm wanting to honor the original design as far as is practicable, whilst dealing with the unruly wiring. I'd like to properly externalise both the crossover PCB's in their own boxes (to sit behind, or maybe even a bit closer to the amp, max of about 1.5-2.5m of wire from each head, one each for left/right).

But more importantly, I need to deal with some unlistenable woofer distortion which only kicks on very VERY low bass and only on the ocassional bass heavy track (even at low listening levels). I'm hoping the recap of the sp1060 with the Alcaps will rectify this problem. The same thing happens with a second set of Mk I B300's I've acquired recently as a backup, and on both drivers. A knowlegable friend thinks the B300's are just kind of old. I'm hoping he's wrong and the unusual high pass filter on them is malfunctioning. Maybe its a bit of both?

By the way, they had a horrific near death experience with a stray forklift prong in transit from Perth to Melbourne (despite wonderful packing by the seller, sloppy careless service from the shipping company nearly destroyed them). See the last picture. By god I was mortified when they arrived like that! Quite a bit of damage to the rear cabinet - now repaired - and what's worse it took a slither out of the main crossover. That was repaired with a wire "bridge" across the gap. Another inch and that PCB would have been cactus.

After that, I feel just so lucky and so priviliged to have them functioning at all.

I'm keen on replacing the little tabs on the PCB's with new ones and crimping wire to them (to hopefully minimise the risk of heat damage to the old boards). I'd also like to use:
(i) a euro strip style terminal block at the head end (will a 6 amp rated one be ok, or 10, or 15?), and
(ii) an 8 way speakon cable and chassis connector from the external crossover box, with cable feeding up through the provided holes bottom and top.

This will enable things to be readily detachable for tweaking and repairs. I'll keep folks posted about my progress here. Its going to take me a while. If we use the crimps they'll take up to 1.25mm wire, enough for 15-16awg which should be fine.

I'd would very much appreciate any guidance on rewiring and other challenges mentioned above. At some stage in the future I wouldn't mind having a go at running them active using some of the better digital crossover/eq devices becoming available these days (waiting for one that can adjust for phase). I'm trying to plan out the rewiring with that in mind, although its in no way an immediate priority.

Well that's more than enough for now. Many thanks for reading, and any suggestions, guidance or warnings much appreciated. I've been lurking/reading here intently for quite some time so I'm pretty sure I've absorbed all the available info, but the "frankenstein" mix of Mk I body with Mk II heads does present some unique challenges, and possibly some novel opportunities.

Any input from this wonderful forum is very welcome.

Cheers to all,
Sandra.
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audiolabtower
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Joined: 06 Jan 2009
Posts: 544

PostPosted: Sun Dec 04, 2016 4:26 pm    Post subject: Reply with quote

Hi and welcome. If you search the posts here there should be a few pictures of my 105s and crossovers. They are certainly worth keeping in good condition. That wood damage is not too bad and should be unnoticeable with a clamp glue and some teak oil. Mine came up a wonderfully rich veneer with that.

You should find some pictures of my external crossovers in the threads which sit under the power amps, they are hard wired direct to the drive units. I used a 30amp screw terminal board on the back of the head unit under the adjuster screw for mid and treble (and indicator circuit) and left the bass connections with large spades and upgraded large 4mm terminals. I wound my own speaker leads using twisted solid core 15A rated for the bass and 2A for the rest. The crossovers were quad wired to join direct at the power amp terminals, but are now separated out for 3 power amps. I would definitely recommend this although "bi-wiring" seems to have gone out of fashion, and the driver side of the crossover seems much less critical of speaker wire than the input side. It also makes multiple power amps easy which I would also recommend with these speakers. If you want to try I can post where to cut and connect the crossovers.

My reference speakers for mid range are still Spendor BC1s, and the 105s are the only speaker I ever found to equal this magical quality with that step up in bass and loudness needed at the same quality level. They certainly beat any LS3/5a on AB1/2 or any subwoofer hands down, and even today stand up against any expensive speaker.
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essem
Introductory Contributor


Joined: 27 May 2016
Posts: 3
Location: Melbourne, AU

PostPosted: Mon Dec 05, 2016 1:18 am    Post subject: Reply with quote

Thanks for the good info audiolabtower. A friend has helped me fix the wood damage and he did a great job; the oiled veneer looks very nice now.

When you say "left the bass connections with large spades and upgraded large 4mm terminals", are you referring to the bass driver itself, as in the picture here: http://rdxx.org/kef/kef105/img/DSC00490.JPG or do you mean where the bass wire connects to its crossover PCB? At the driver, we've done an interim "faston" crimp (in Australia these seem to be called "Quick Connects") to the 2.8mm sized tab on the woofer; are you saying that terminal (which looks like a square U) could be replaced with one that can take 4mm spades, thus allowing bigger gauge wire?

For the PCB's, I've ordered some new solder tabs but couldn't find any bigger than 2.8mm with just one leg. The 4mm and up ones have two legs -- should I get those bigger ones and just snip off a leg? I mean "PCB tabs" pictured here: http://www.molex.com/molex/products/family?key=pcb_tabs

Forgive the bubs level questions; my soldering skills are rudimentary and I'm nervous of causing heat damage to unobtainium PCBs and driver terminals. Happy to get the right parts and if needed take it to a pro to do the risky soldering bits. With fresh bigger tabs on the boards experimenting will be easy.

Using multiple power amps is a fair way off in the future. But a related bi-wiring question... I'm running 4 core Mogami 2972 speaker wire from my amp. Is it advisable to hook up 2 of those incoming cores directly to the bass PCB's inputs, thus replacing the soldered wire from the main PCB to the bass PCB?

Cheers, and thanks. S.
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audiolabtower
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Joined: 06 Jan 2009
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PostPosted: Mon Dec 05, 2016 7:01 pm    Post subject: Reply with quote

Hi again, I meant the bass unit connection terminals on top of the box by the tube for hiding speaker wire. These are a larger screw type with large gold spades from the crossover/amp. I soldered wire direct from the bass drivers tabs to the terminal undersides inside the box. personally I replaced the internal wire with something a little more substantial to get resistance down as much as possible. From your picture you don't appear to have the terminals on top of the bass box. Those holes will need filling with something to get a closed box response. The mid treble crossover originally had short (few inches) leads to 4mm terminals (red and black) which connected to the 4mm screw terminals on top of the bass box and thus also the speaker leads.

Those tabs look fine, whatever fits ok.

If the crossovers are to be mounted somewhere secure you could consider soldering the cable direct to the pcb through the terminal hole getting rid of a number of push on connectors in series with the signal. These can oxidise in time and may start to degrade contact possibly. But if a beginner with soldering maybe the tabs would be more suitable meanwhile.

If you have 4 core speaker wire, I would use 2 cores for the bass unit crossover and the other 2 cores for the head unit crossover, joined only at the source speaker terminals on the amplifier. Thus you don't need the connection from the mid/treble crossover to the bass crossover at the speaker anymore.
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essem
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Joined: 27 May 2016
Posts: 3
Location: Melbourne, AU

PostPosted: Tue Dec 06, 2016 10:41 am    Post subject: Reply with quote

That's extremely helpful info, much appreciated.
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