It's the fly-back transformer. For TV CRT's it's around 15kHz, monitor CRT's are higher. https://en.wikipedia.org/wiki/Flyback_transformer https://en.wikipedia.

It's the fly-back transformer. For TV CRT's it's around 15kHz, monitor CRT's are higher. https://en.wikipedia.org/wiki/Flyback_transformer https://en.wikipedia.org/wiki/Flyback_transformer.