Fine tweeter wires won't solder

[emeritus]

Good stuff, solvent-based Evostik. In the 1960's I repaired a damaged paperback book by applying Evostik to the spine, (something I still use it for) and the more than 50-year-old repair is still flexible and holding the pages securely in position. I just hope they haven't had to change the formulation significantly on H&S grounds. I hadn't thought of using it for your type of repair: looks like it would be easier to apply, and set faster, than silicone rubber.

[stevehertz]

So far so good. Following my planned procedure (in my previous post) I managed to solder on the two lengthening copper wires using the Alusol. I then 'tied' one of the joints with a single, knotted wrap of very fine copper wire for extra strength. Due to the extra 'bulk' that this procedure adds to the joint, I was unable to do it to the shorter wire where the join (unfortunately) lay right under the flat mounting rim of the tweeter membrane. In fact I had to cut a small, narrow nick/section out of the membrane at this point so that it was able to lie flat on the magnet assembly. However the bead of Evostick that I used to stick down the rim meant that this nick and the wire passing through it are all nicely secured. Gluing the membrane down was difficult as I had to make sure that the voice coil was central in the magnet gap. I had drawn pencil lines before removing it though, mindful of needing a visual aid for re-assembly. I then replaced and bolted on the plastic mounting plate having first cleaned off the old solder from the terminals. I then soldered the lengthened wires to the main terminals making sure that I did not linger, so as to avoid possible de-soldering of the lengthening joints that are just a couple of cm away.

Checking the tweeter on an Avo it makes the requisite clicking and scratching noises, so with a bit of luck and a following wind, it will work in the speaker. The only worry is that due to the handling and bending that the two wires from the coil have undergone, they may break once exposed to the constant vibration of the voice coil in use. We'll see..

[crackle]

I have had exactly the same problem on a diaphragm I repaired. It looked tinned but would not wet with fresh solder. I felt the wire was aluminium but copper covered but if you tried heating it too much the copper was etched/dissolved away.
I had just enough to cut back and start again, and did manage to get the solder to take.
Good luck, don't melt the diaphragm

Mike

[stevehertz]

The tweeter is now back in the speaker, and I'm glad to report that it works fine. A success. So far..

Thanks guys for the interest, input and suggestions. This was possibly the most difficult single piece of repair/restoration that I have undertaken in over 40 years messing around with vintage audio visual equipment. I've previously done electro-mechanical 'open heart' surgery on video machine where a few microns can make the difference between video and a blank screen, but nothing as taxing as this. Although my repair explanation - to an extent - makes it sound relatively straightforward, the fragility of the parts, their close proximity, and the general inability to 'get to grips' with things made performing work difficult, and many individual parts of the repair had to be repeated many times, often using a different approach, not only to simply 'make it happen', but to avoid damage to the membrane or coil of the tweeter.