It's a Dual-Gang pot with one section C10K and the other section A250K. EG sells 'em. I've picked up a couple dozen when they went on sale. Could be useful for filters, gain controls, LFOs, etc.
Some kind of tube preamp that brings in more mids/light bass cut as you bring up the volume? And could they work opposite - wire the C10K 3-2-1 and the A250k 1-2-3?
That will have a much smoother sweep at each end of the GAIN pot's travel. One thing, it's necessary to adjust the values of the 10K, 220K, 6.8K & 100nF in proportion to the C10K pot.