0A2 + 0C2 = 150 + 75 = 225 0B2 + 0B2 = 108 + 108 = 216 among others; some VR-tube voltages (90, at least) were not made available in miniature-tube form. Some regulation-voltage values are generally more stable than others as a result of the different gas mixtures used; the regulation achieved is still much better than that possible with a resistive voltage divider. 0B2s will usually stay close to 108 V. "75 V" regulators may be somewhat off 75 V. The regulation voltage varies from tube to tube, and voltage to voltage, and with aging. The regulation, rather than the exact voltage level achieved, is the important thing. Overcurrent/overdissipation can spoil a VR tube's ability to regulate properly fairly quickly.