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Orion VFO Tuning Encoder - Part numbers
This is the original tuning encoder, which is no longer available: Oak Grigsby 94Q 125-02-00606
These are possible alternates, but no verification that they will work:
Bourns ENT1D-B28-L00125L (also believed to be obsolete)
Avago HRPG-ASCA 17R (this would probably work electrically but the threaded collar on the shaft is narrower than the Orion mounting bracket)
Iwatsu EC202C128A-2TD-0277 (Ten-Tec reportedly used these in later production but it is not known whether the threaded collar is the same size as the Oak Grigsby).