Tube Driver cap question (is it really this low of a value?)

[midwayfair]

Looking at the GGG tube driver schem, C6 caught my eye:



Is ... is 10n really correct there? That seems REALLY small, putting the cutoff at 1.5KHz. Or does sending it to V- change what I need to use to calculate the cutoff frequency? Or was this done to brighten up the circuit because the tube is starved?

[PRR]

> cutoff at 1.5KHz.

800Hz.

The "R" is 10K+10K = 20K.