Miller capacitance at valve input

[untune]

To tie this up: abbey road was exactly right, it was a short. I'd nicked one of the (extremely thin!) signal wires with the knife when I cut the outer sheath back. Twisting the shield tight had put them in contact hence no signal.

All working fine now, used a pair of 51k resistors as stoppers giving 25.5k in parallel. Worked out for a cutoff around 40khz. No noticeable high end rolloff, all sounds good! Thanks for the help