Some voltage-regulator tubes contained small amounts of radionuclides to produce a more reliable ionization.

For instance, voltage-regulator tubes contain various inert gases such as argon, helium or neon, which will ionize at predictable voltages.

Types such as the voltage-regulator tube and thyratron resemble hard vacuum tubes and fit in sockets designed for vacuum tubes.

A voltage-regulator tube (VR tube) is an electronic component used as a shunt regulator to hold a voltage constant at a pre-determined level.