Gibson BA15-RV Bass Control

[separateness]

I've been wanting to build a small bass amp and have been perusing various schematics and I came across the attached bass control.  I was hoping some one could help me parse what is going on here.
What I think is happening is that negative feedback is being sent from the plate to the grid via the 10nF cap through two 470kΩ series resistors.  Between those resistors we have our bass control. Ignoring the pot for a moment, the feedback signal seems to be -8dB in its passband and starts to drop away at around 130Hz. So the pot basically controls this sub ~130Hz negative feedback.  Turning bass pot 'up' (ie towards the 470kΩ resistor) shorts the feedback to ground, so the bass output of the triode is thereby increased.
Do I have this right?  This seems like a very, very cool bass control. Information on this amp seems to be scarce as hen's teeth