I have a ST-120 that is about 3 years old. It still has the VTA driver board that came with the kit. I see now that there are new driver boards out that use a constant current source rather than the old trimpot controlled AC balance system. I have 2 questions:
1. Is the constant current source a big enough step up to warrant an upgrade.
2. If it is worth upgrading, should I install the board that takes 6sn7's?