The problem boards VTA ST-70 with LM334 is solved! CCS Zero temperature coefficient current source for tube phase Inverter

from ieLogical LM334Comp

All VTA designs using the LM334 for the Phase Inverter tail suffer thusly: long warm up time, temperature sensitivity and balance instability. This can be remedied very easily.

Due to the LM334 instability, the Phase Inverter gain constantly changes, and as a consequence, the image wanders. The amps never reach equilibrium.
At a minimum, move the compensated LM334 to the underside of the driver board. Note the orientation of the compensated LM334. On the bottom, the LM334 rounded side is toward the transformers. Mounting under the board will prevent some heating by the tubes, helping to stabilize thecompensated LM334. The current may not achieve design values quickly as the internal chassis temperature rises slowly.

For the Temperature Compensated Full Monty:

CCS parts go on the PCB underside as shown. The amp now very stable. With compensation, the LM334 stabilizes rapidly and does not drift. Sonic image now remains rock solid. Phase splitter balance is surprisingly good, tracking perfectly from naught to clipping.