Tube DIY Asylum

Posted by TimFox (A) on April 21, 2012 at 12:46:58

In Reply to: RE: Digital substitute for OA2 posted by Lee of Omaha on April 21, 2012 at 08:06:45

Every circuit using a VR tube requires an initial high voltage to start the tube. Extra resistors need to be added when VR tubes are in series to ensure they all start. For the 0A2, the initial voltage must be greater than +185 V (with the tube not conducting), with a nominal 150 V sustaining voltage after starting.
I agree that a series string of 5 V zeners is quiet, with a reasonable temperature co-efficient. A single 150 V zener has a relatively high temperature co-efficient. However, reference glow tubes, such as the 0G3, have quite good co-efficients (-2.7 mV/K, or 32 ppm/K of the 85 V reference value), but the temperature co-efficients for general-purpose tubes such as the 0A2 are not specified. However, the oG3 and similar reference tubes need to be run at a fixed current, and are not suitable for general-purpose shunt regulators over a wide range of current.