Neon sign transformers are used to power neon signs. There are two main types Electronic and non-electronic.They come in a range of wattages (100W to 1.5Kw) and voltages ( 5Kv to 15Kv)
The electronic ones use a switch mode power supply and current monitoring circuits to control their output. For experimental use the electronic NST’s are too delicate to be to much use. Or though it is possible to use them with care.
The non electronic NST’s are a shunted transformer usually potted in to a steel or plastic case. Because of this potting compound it is not usually possible to remove the current regulating shunt, so their use for higher powers is limited. They do however make excellent supplies for small tesla coils.
Some NSTs have built in electronic earth leakage trips that can limit their experimental use.
The output from an NST is LETHAL
NST’s are also prone to failure from over-voltage, and a filter and safety gap is recommended in tesla coil use.