There is a clear correlation between increased NMR bore temperature and a concomitant decrease in NMR coil heater power. The bore temperature seem to increase when higher sample temperature is set say above 25C. The preamp heater power is quite stable.
bore temperature/NMR coil heater/preamp power
301.86/17%/146% sample temp 25C
304.89/15%/145% sample temp 28C
305.04/16%/148% unknown sample temp (must be close to 28 C)
309.13/14%/147% sample temp 32C
327.34/7%/146% unknown sample temp
The temperature gas flow is 670 L/h.