Electrodynamic Speaker Repair
I did a restoration on a STC Model 430 and it was going quite well, I generally run them for about a month before I would put it up for sale. Then all of a sudden about 2 weeks later I would get a slight drop in volume and then it would come louder again. This went on for some time. I checked over the chassis many times just going over and re-going over, thinking is there something I have missed. Then I found it, a wire that had never been soldered to the speaker terminal. Woo Hoo I thought, that'll fix it, so I ran the set for another week and just bumped it and the sound dropped again, well a few words came out. I started looking at the speaker again, have I done something ? Then there it was, this is it for sure ! See in Picture 2 & 3 where I have used 2 black heat shrinks and some heat sleeve on the wires coming from the top single coil. The insulation had worn through enogh to be earthing where it comes through the small hole closest to the speaker basket. I really had no choice than to cut the rivets off and repair it properly and as you can see in picture 5 the voice coil copped a beating, so I had to make a new one. Picture 7 Shows how many attemps I had before getting it right. The original craft paper was too thick, so I tried 80GSM paper and that was too thin. "Starting to sound like the 3 little bears", anyway I ended up using 120GSM craft paper from "Officeworks" if your in Australia with 30minute epoxy and a 19mm dowl from Bunnings. I can say now that it is working very well. The voice coil in Picture 9, the coil looks distorted but it's a thin blue texter mark that I used to align the coil with the top of the coil gap.So I hope this info can help other vintage enthusiasts. There are some great videos on YouTube for voice coil making and reconing. It's not that hard, you just need the right size former and patience, oh and the right type of speaker cone and spider.
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