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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 is currently available and a good bet since the Avago HRPG-ASCA 17F is used in the 302R remote tuning knob)