So, you have relatively clean signal at R4, but not at pin1 of IC1, correct?
Your VR voltage seem to drop off some after the two 1M biasing resistors, R2 and R4. Both are 1M. So, couple things come to mind: 1) your DMM is acting as a voltage divider when you measure those spots making the voltage appear lower, 2) you did not use 1M for those two resistors, 3) something is wrong with the resistors, 4) the pinout of your 2SK170 is not DSG.
Your VR voltage seem to drop off some after the two 1M biasing resistors, R2 and R4. Both are 1M. So, couple things come to mind: 1) your DMM is acting as a voltage divider when you measure those spots making the voltage appear lower, 2) you did not use 1M for those two resistors, 3) something is wrong with the resistors, 4) the pinout of your 2SK170 is not DSG.