It does drift away as it warm up though. It can start out as +/- 0.5 or 0.9V and hang around +/- 50mV after 10 minutes. But then after 20 minutes or so, it would hang around +/- 125 to 320 mV. I will check again today
I have used the opto servo in one T2 and one grounded grid for quite a while and that servo works very well. The offset is mostly in mV range. I can’t tell if it effects the sound negatively.
Offset within 30 or 20 volts is not much to worry about with an electrostatic amplifier with only trimmer/resistor. 1.5V is very good.
If your amplifier has an opto servo then 30 or 20 volts offset is abnormal, even 1.5 V tells you that the amplifier is’t working properly.
No, the numbers are not great. For an opto servo they are normal. Well done!