More evidence on low cathode temperature, low anode voltage merits

Quoting from the Pearson paper:


"...Noise measurements were also made on the No. 259 tube with its control grid floating at equilibrium potential. Using the operating voltages specified above, the noise level was about 20dB higher than those given in Table IV. The level can be greatly reduced by operating the tube at a lower cathode temperature and with lower screen and plate voltages. [14] the reduction in noise is due to a decrease in current to the floating grid. Using a heater current of 1.3 amperes, a plate current of 0.1 milliampere, a screen potential of 16.3 volts a plate potential of 30 volts the equivalent input noise was 1.4 x 10 to the -5 volt for the entire range from 10 cycles to 15,000 cycles. Under these operating conditions the floating grid potential was 1.0 volt negative with respect to the cathode, the input resistance 1.4 x 10 to the power of 10 ohms, the dynamic grid to cathode capacitance 6 x 10 to the power of -12 farad, and each compnet of grid current about 4.5 x 10 to the power of -12 ampere."


References:


Fluctuation Noise in Vacuum Tubes - G. L. Pearson
https://ia800308.us.archive.org/21/items/bstj13-4-634/bstj13-4-634.pdf


[14] G. L. Pearson is indebted to Dr. J. R. Dunning of Columbia University for pointing out this fact.