Altair FDCplus Floppy Disk Controller
Altair FDC+ Floppy Disk Controller
"The Altair FDC+ is an enhanced version of the original MITS floppy disk controller for the Altair 8800. The FDC+ is a 100% compatible drop-in replacement for the original two-board Altair FDC. The FDC+ can serve as a replacement for a missing or defective Altair FDC, or you can use the FDC+ as a reference point while restoring original floppy equipment to working condition."
Read more about the FDC+ at the official DeRamp site.
I purchased this PostEra Altair compatible FDC+ card fully assembled. It has a serial disk drive emulator that I've used. It's very handy for troubleshooting vintage Mits Altair computers as well.