It'll find a test home in my tweakers amp which is currently a c3g parafeed. By the way, the c3g ccs loaded parafeed is currently biased by a tl431.... i think i prefer it to leds!!! the bass seems better... which could always be a small change in operating point.
its adjustable upto 36v (max rating) and achived using a couple of resistors - the datasheet explains better than i can. Watch the power rating though, it soon falls off with increased temp. Another thing to add is that i have a slightly increased noise floor with tle431, not noticable with senns but is with grados. I am looking for an osciallation but cant spot one, but my scope is a bit rubbish. The c3gs and d3a LOVE to oscillate, i doubt this would be a problem on non 'extreme' valves.
another method that would probably yield better reults is using a pnp in emitter follower.. you get the stable vref from the leds and the low dynamic impedance of the pnp - you can also scale power requirements with pnp type. cathode voltage = vref + Vce(which is about 0.7v)