They are gradually replacing iron cored transformers in neon signs.
2.
It has a circular cross-section due to a poloidal graphite limiter and an iron core transformer.
3.
They use an iron core transformer to provide a suitable high impedance load to the valve ( s ) while driving a speaker, which is typically 8 Ohms.
4.
These generate the same voltage and current ranges as iron cored transformers, but in much smaller, lighter designs at high frequency ( not the common 50 60 Hz ).