Please post your new readings for bias voltages.
When it's turned up, is it as loud as you'd expect? If possible measure the output. Maybe you have a build mistake, so check the components that you have in your own layout against the drawings to make sure you haven't got parts transposed. It's easy to overlook something when you've been staring at it for long enough. You say the voltages are where they should be - have you measured the critical voltages through the preamp - that is, plate and cathode for each stage?