Gas tubes produce noise, but not as high as some zeners. However, if bypassed by too much capacitance, they will turn into relaxation oscillators! The tube data books specify a maximum recommended capacitance, typically 0.1µF for the 0A2 and 0A3 regulator families and 0.02µF for the 5651 reference type. In circuits that use the gas tube (or zener) as purely a reference (no current drawn by the load), an RC filter network with a time constant below the audio band can effective eliminate the noise. If some current draw is required, a cathode follower buffer can be added, as shown in fig. 2.

to .005% per °C - much better than high voltage zeners, and competitive with the better IC references. Neon bulbs are symmetrical, so can be connected in either direction in a circuit, but other gas tubes must be connected with the proper polarity.
    The failure mode of gas regulators and references is lowering gas pressure due to "clean-up" caused by electrons and ions trapping gas molecules in the metal structure. If the tube is run too hot or overloaded then active gas molecules such as oxygen or hydrogen are liberated and the gas breakdown characteristics are degraded. If gas tubes are run near the low end of their current range, they should have a lifetime much longer than the vacuum tubes they are used with. However, rather than dramatically failing, they usually slowly lose regulation, so should be checked if they have a lot of hours on them.
   Gas regulators do not have very good dynamic response. Due to the time lag of the heavy ions that make up the discharge, they have time lags in response on the order of tens of microseconds. Redistribution of the discharge in the tube can make them even more sluggish. For this reason, they should not be relied on to stabilize strong audio-frequency variations.