diytube.com

I'm geting ready to rebuild two Dynaco ST for someone esle with the
diytube stereo 70 driver boards , and the owner wants to use 6550 inplace of the EL34's .Would there any advantage to tieing the bottom of the LM 334 current scource to a -40 volt supply similar to what David Gillespie did in in his mod to the Eico ,where the resistor of the long tailed pair was tied to a minus 70 volts to get more drive for 6550s .



http://www.tronola.com/html/hf-60_with_6550s.html

Looks alot like Kara Chaffee's Mark III mod, except she uses a 12AT7 front end. If you use the LM334Z and the higher plate resistors (62K) you'll get even more gain, without the negative power supply.
6CG7s might work better as a SRPP, with the slight bit more gain, than paralleled. Wonder if you can direct drive V2 with the center connection of a SRPP?

The LM234Z/LM334Z only is rated for 40V, so your -supply would need to be much smaller. For your application, I don't think you need it.

I like to see the voltage drop across the CCS at around 8V to 12V, so you can adjust the current set resistor as needed if you ever change the plate resistors.

Shannon