Anyone know of a replacement midrange around? Hopefully a JA-0701B from a 690II, but would consider A or C versions too.
If it wasn't already explained, my understanding is that while the tri-amp version was available with the Mk1, it wasn't standard. So most Mk1 690s will not have the tri-amp capability, ie. yours. Also while some of the 690IIs have a vented cap woofer, most do not, and I don't think any are plywood.