Electro Voice 667a (668) disassembly?

[OneRoomStudio]

I picked up an EV 667a for a good price, but it needs a little restoration. Anyone know how to get into these? I know how to access the switch-pins at the rear of the mic, and I know how to remove the grill (same as every other EV mic), but I can't figure out how to get into the body.

There's some info here: https://www.coutant.org/667a/index.html
and here's the engineering data sheet: https://products.electrovoice.com/binary/667A Engineering Data Sheet.pdf

Anyone have any other info?

 

[OneRoomStudio]

Well, I figured out how to get to the diaphragm. Unfortunately, I also found that one of the magnet wires to the center coil was hanging on by a thread, and it broke just as I pulled the protective mesh screen off. I'm guessing I'm SOL now. Does anyone have any magic ideas for repairing it at this point? @panman maybe?

 

[panman]

Well, proper pics from the situation might help to assess, what can be done.

 

[OneRoomStudio]

Well, proper pics from the situation might help to assess, what can be done.

Thank you! It's a bit difficult to see, but if you look closely, you'll notice that one of the green coil wires has become disconnected from the coil. It broke right at the surface of the diaphragm, so there isn't enough wire left to solder to.

 

[panman]

It would be necessary to unglue and remove the diaphragm undamaged. Not easy. Then the voice coil needs to be removed from the diaphragm. For that you really would need to be lucky. Choose the wrong solvent for the glue and the diaphragm melts or the coil falls apart or nothing happens. In case of unlikely success, it might be possible to pull out the coil-end, but most likely not. But again, in case of success, good luck glueing the coil back on the diaphragm. Forget about pulling the coil-ends through the diaphragm, but leave them underneath. If you have gotten this far, having replaced the shims destroyed, when removing the diaphragm, you need to glue back the diaphragm correctly wthout any coil-rub and also sounding right. But before glueing you should first solder the coil-ends on terminations. Usually on EVs the coil was aluminium. Great! Good luck with that! Besides beeing brittle, the solder does not want to stick and connect, because of the very fast oxidisation. It was along time ago I done it and I do not recall anymore, if it was some acid or special flux, that can be used, but I remember failing a lot.

I know this hurts, but the costs of all the above would clearly be huge and the result most likely a failure.

The only chance I see for it, is to find a replacement voice-coil/diaphragm. Many other EVs have the same diaphragm and the thing is to find one in a mic broken otherwise or at least the voice-coil easier repairable.

 

[OneRoomStudio]

It would be necessary to unglue and remove the diaphragm undamaged. Not easy. Then the voice coil needs to be removed from the diaphragm. For that you really would need to be lucky. Choose the wrong solvent for the glue and the diaphragm melts or the coil falls apart or nothing happens. In case of unlikely success, it might be possible to pull out the coil-end, but most likely not. But again, in case of success, good luck glueing the coil back on the diaphragm. Forget about pulling the coil-ends through the diaphragm, but leave them underneath. If you have gotten this far, having replaced the shims destroyed, when removing the diaphragm, you need to glue back the diaphragm correctly wthout any coil-rub and also sounding right. But before glueing you should first solder the coil-ends on terminations. Usually on EVs the coil was aluminium. Great! Good luck with that! Besides beeing brittle, the solder does not want to stick and connect, because of the very fast oxidisation. It was along time ago I done it and I do not recall anymore, if it was some acid or special flux, that can be used, but I remember failing a lot.

I know this hurts, but the costs of all the above would clearly be huge and the result most likely a failure.

The only chance I see for it, is to find a replacement voice-coil/diaphragm. Many other EVs have the same diaphragm and the thing is to find one in a mic broken otherwise or at least the voice-coil easier repairable.

I thought that was the case. Thank you for confirming. I read a rumour somewhere that RE-20 diaphragms will work in these, but I haven't been able to confirm that.