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