What's happening here?

[tubenit]

I've not seen a cathode cap/resistor set up like this before?  Anyone know what's going on with this?

With respect,  Tubenit

[LooseChange]

Yes you have. Look at half of a long tail PI.
It provides fixed bias to the tube.

[John]

What are the advantages to that over the simple cathode bias we normally see on preamp tubes?

[Colas LeGrippa]

the last section to ground ( 3.9k / 2,2uF ) is a typical low-pass filter arrangement

[PRR]

> low-pass

At 18Hz. Won't affect small-signal response. Might be overload-recovery timing. Might be a waste of 3 small parts.