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Old 6th September 2019
  #50
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MK221 repair details

This is an old thread, but just so there is information in the archives for future inquiries I'll post a few details. Nearly every time a microphone capsule is repaired, if it's done correctly, the entire new microphone manufacturing process must be followed. For inexpensive mic capsules that are made to wide tolerances, the parts just go together and it's fine. For designs that require tighter control of material properties, it can take several weeks of aging to assure that the performance is stable. That's why we maintain a few rebuilt MK221's for C617SET mics.

As noted in this thread, MK221s with the Josephson logo are selected to our specification. Gefell tolerances are already very tight, we just want to be sure that any two C617SETs match closely enough to be a stereo pair so we have picked a window out of their normal tolerance. If the backplate is not damaged, even a new diaphragm should result in the same response, and frankly any two undamaged MK221s are probably close enough for stereo, just maybe not close enough for us.