if you want really good regulation,
you still can't beat the venerable LM723.

Note that I really need an absolute minimum of 2A current handling, so
LM723 is out and LM317 is too marginal - tubes need between 1.25 and
1.75A.

No virtue in batteries, and a pig to implement. I have tried, but a
good current source sounds just as good as long as you can get the hum
right down.

Keep the suggestions coming!! Andy