SP-70 Dead Tweeters

[Trw]

 

[Mr_Mustrd]

If they are open circuit,it'll be the voice coils which can be rewound/resoldered.

I fixed up four klh model sixes that was rescued from the dump and one of the four had a bad tweeter. I already bought a replacement at the time so I threw caution to the wind and tried to fix the bad tweeter by soldering the thin coil wire and ended up screwing it up, had a really hard time getting the solder to stick. This time around I have a little better soldering iron and little more soldering experience so I'm not opposed to trying again. Any idea on how to safety open the tweeter? I see 4 screws in the middle but I didn't know the best way to pry it open to get to the wire

 

[Peter lye]

Any idea on how to safety open the tweeter? I see 4 screws in the middle but I didn't know the best way to pry it open to get to the wire

my Sea tweeter look similar to the T1001 tweeter design.
Here what inside, that will give you some clue.

 

[Mr_Mustrd]

Was able to get it open. Took some photos. I think i see where it's disconnected. Would that be what I'm trying to solder?

 

[Sansuiman]

That would be the spot. The tricky part is tacking it together while not creating a "blob" that will rub or interfere with the free movement of the diaphragm once reassembled. It should be doable, but will certainly be a delicate operation. If you can salvage those, it would be an outstanding bit of work.

I've done similar work on a couple of Sansui cone midranges, where the lead out wires from the coil to the basket terminals were open. Damn near microsurgery level work to do without botching it up worse. Requires patience, a steady hand and a sharp eye.

 

[Trw]

To add to that..you may need to very lightly sand (fine grit) and carefully tin the wires pre soldering.
Prep is everything

Good luck,fingers crossed for you

 

[Sansuiman]

@Trw raises an important point. Coil wire is enameled to insulate it from shorting against itself, and the enamel must be removed before soldering.

 

[Mr_Mustrd]

Unfortunately the wire broke as soon as I touched it, it wasn't freely moving and was stuck onto the side . Would it be possible to patch it with some replacement voice coil wire? I have nothing to lose at this point. I'm thinking if I could find the right diameter, it could be doable.

 

[Sansuiman]

If you can find proper gauge coil wire, it may be possible to effect a repair. My guess is the tweeters were over driven at some point, heating up the voice coil, which damaged it and is what caused the open in the first place. Not that such small coil wire is very strong to begin with.

 

[Mr_Mustrd]

If you can find proper gauge coil wire, it may be possible to effect a repair. My guess is the tweeters were over driven at some point, heating up the voice coil, which damaged it and is what caused the open in the first place. Not that such small coil wire is very strong to begin with.

Thank you for your time! I'll see about hunting down some coil wire and give it a shot. Who knows? Maybe I'll get lucky and it might work, but either way so far its been a fun project.

 

[Sansuiman]

If you do get a repair to hold, it should be coated with something to insulate it. Perhaps nail polish or some such that can be brushed onto The soldered repair. Otherwise it runs the risk of shorting to another metal surface

 

[HTRDoug]

I don’t know if it is possible due to the frailty of the old wires but if the break is at the last turn of the winding as it looks maybe you could unwind one wrap and prep and solder it outside of were the coil rides in the gap, it wouldn’t cause a noticeable different in the performance of the voice coil being only 1 turn. Alternatively you could watch some videos on making voice coils and rewind it completely.

 

[mikenelson]

According to the tech who repaired the midrange voice coil from my hpm 200s said it's very critical to match the weight of the replacement wire to that of the voice coil wire. He also said the same of the solder and he also used a specialty rosen that had been developed by Nasa. Alternately You could contact The Vancouver audio speaker clinic and enquire if they have any old stock voice coils. They just did a complete woofer recone on my rare set of 1970 set Panasonic sb-400s, they also ordered in voice coils from one of their sources for the woofers so it is possible there is a source.

 

[Mr_Mustrd]

New tweeters came in and have them installed. They were almost a perfect drop in, but I had to cut a very small notch on the left and right for the positive and negative terminals of the tweeter to allow it to drop all the way in to make it flush with the cabinet. Because I didn't have to modify the baffle that much I can swap back to the old tweeters without compromising the seal. It didn't come with screws so I had to make do with what I around, and I didn't want to reuse the threaded sockets from the old tweeter for when I hopefully can switch back to the original tweeters

Haven't had a chance to really tested them thoroughly, but initial impressions are I really like them, and as a bonus the wife wants to keep them , she was on the fence of selling them. They lack the bass of the ola or ARax2 that I have but, I knew before buying them that would be the case, but overall I do really enjoy them, I have read that using acetone to loosen the surrounds and then follow it up with doping from ar vintage? I do have a bottle of that around and could try that.

The one on the left has been recapped with audyn cap plus and the one on the right still has the original caps and switching from left to right I can really tell a difference, it's not subtle difference either. The one that is non capped is muted and muddy sounding were as the recapped sounds bright and has a sparkle to them, its almost like the speaker has come to life and the non capped one is struggling to breath. They are powered by the SX-636 that I've rebuilt that is waiting on new filter caps, but I plan on having the SP-70s ran by my Sansui 2000x that I want to rebuild as well once I finish my ever growing list of projects.

Thank you everyone for the help and suggestions! I've reached my budget cap to spend on this at the moment, but eventually I would like to either try to find another pair of SP-70s that I can salvage tweeters from or getting the right voice coil wire and trying to repair the old tweeters. In the meantime I’m very pleased with this change, the new tweeters looks clean and flush with the cabinet and as a bonus I can swap back in the original tweeters without a problem.

 

[Trw]

I think you may be surprised by their bass capabilities on the end of your 2000x mine dig deep with my model 2000

 

[Mr_Mustrd]

Well looks like I spoke too soon, the speaker that has been recapped, the tweeter is not working, the speaker that is still original the tweeter is working fine. Was going to give it a good listen today because I'm off work and in double checking everything I'm getting no sound from the tweeter. I took everything back out, measured the tweeter and I’m getting 7ohms, even plugged the tweeter into the positive and negative where the woofer goes and I get sound that way, so the tweeter is working and the wires connected to the tweeter are connected to the correct positive and negative. I deoxited and faderlube the pot but no change. I checked the resistence of just about everything and nothing is open, both of the new caps are measuring 7ohms with the woofer connected and tweeter disconnected. Its such a tight fit to get those caps in there so the caps aren't touching anything as far as I can see. Any ideas on what to check next? Could be a bad pot? Are the new caps causing the problem? The new caps are the same capacitance as the original, 3.3uf for the woofer and 2.2uf for the tweeter, but the voltage is higher. I could put the old caps back in but would like to not do that considering it was a pain to get the new ones in there. Also could get another crossover from ebay as well which if is the pot i'll have a replacement.

 

[Sansuiman]

I'd check the control (not really a pot, but a rotary switch) as it still looks badly tarnished in the picture. Also make certain the fixed contact points are properly gapped such that they are making with the moving contact to complete the circuit. It doesn't take but the thinnest of over-gap to break the circuit.

These can be a bit temperamental, especially if someone has previously messed around with the switch and the fixed contacts were bent even slightly out of shape. May need to continuity test all poles of the switch to be sure it is passing signal.

 

[Mr_Mustrd]

Figured it out! While checking on the switch and the contact points I opened up the working speaker to also check the switch and I found that the 2.2uf cap was connected to the wrong spot! I'll never learn that it's always the simplest of things that cause problems rarely the complicated. Thank you @Sansuiman You've been a huge help! Now onto putting this one back together, recapping the other speaker and I'm gonna enjoy this weekend listening to them with my sansui 2000x

 

[Trw]

Agreed it's usually something and nothing!..
I'd be curious if your original tweeters may work now having reflowed all of the solder joints,cleaned switches etc (unless they were both o/c).
Looking forward to your review.

 

[Sansuiman]

@Trw, posted upthread was a picture of one disassembled, clearly had a break in the coil wire coming off the former. Suspect condition of the other one is much the same as they both measured open.