SK2-V 008059 with new matched (<10mV) 6SD4 nuvistors. 3-20-6

supply  vout    vinm  vinp=0V after warmup stabilization. Gain=20x, Rf=2meg,Ri=100k

300  909mV   43.3mV  

250  303mV   14.6mV  

200  142mV   8.3mV   

150  619mV   29mV    

100 1680mV   79.6mV  

50  1101mV   29.9mV  

25   710mV   20.0mV  

The following plot shows that the input and output offset voltages don't track very well at low supply voltages. Perhaps something to do with the behavior of input leakage currents on the 2Meg feedback resistor.