You just pull the old board and replace it with the new board. You also remove the two old 15.6 ohm bias resistors and replace them with four new 10 ohm resistors (supplied with the VTA board and parts set). You pull both resistors off the quad cap and replace one with a jumper wire and the other with a 2200 ohm resistor (supplied with the parts set). You can also remove (or leave in place) everything on pins 1-4 on the 7 lug terminal strip, the present selenium rectifier and the two original bias pots. You will also need three 12AT7 tubes. There is a short manual that comes with the board and parts set. It gives you simple instructions how to install the board. It's not that hard to do ...
If you are interested in getting a VTA board and parts set for your ST-70 just send Roy Mottram at the tubes4hifi web site or myself at Bob01605@aol.com an Email and we can give you more particulars about the board. This board will make a noticeable improvement in sound quality over your stock Dynaco driver board with the 7199 tubes.