Increasing voltage from a neon sign transformer
You can probably overdrive the primary of the NST by about 10% or so without running into problems. There are a number of ways to do this.


Most Variacs (variable autotransformers) are capable of producing about 10% over the input at their maximum setting.
A 12.6 V filament transformer can be wired as an autotransformer to give a fixed &plusmn;12.6V offset (i.e., about &plusmn;10% @ 120 VAC nominal). Note that the current rating of this transformer's secondary must meet or exceed the primary current of the NST.








simulate this circuit &ndash; Schematic created using CircuitLab