Using a plain old VOM, I trace good response (test tone at 100hz) to the socket grid connection of the driver tube, a 5687. The 5687 has 170v on the plate (pin1), the cathode is at 7v(pin 3), running at 14.7ma. I measure a 5v RMS signal at the grid pin socket connection (pin 2).

There is little or no signal appearing at the plate (91mv).

Swap in several different tubes, 5687, 7044 no change.

Any ideas?

Rk=475r (bypassed 220uf) Rl=7k5 Grid=100k gain pot