# High Voltage NST - Playing with the Frequency

## Main Question or Discussion Point

When I plug my NST into the wall at 60 Hz, I've been told a 120 Hz AC current comes out of my NST. What happens if I modulate the input frequency with a function generator to the transformer?

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berkeman
Mentor
What's a NST?

A Neon Sign Transformer

The performance of NST at different frequencies will depend on the transformer core.

The higher you go in frequency, the less of magnetic flux will be absorbed by the core, and hence less flux will transfer to the secondery winding giving an overall greater power loss.

berkeman
Mentor
When I plug my NST into the wall at 60 Hz, I've been told a 120 Hz AC current comes out of my NST. What happens if I modulate the input frequency with a function generator to the transformer?
Why do you want to do that? As waht says, the 60Hz transformer is really only built to transfer power near 60Hz. When you get much above 60Hz (say an octave or two probably), the losses in that 60Hz transformer are going to get big.

EDIT -- BTW, a real good way to melt a 60Hz transformer and almost catch it on fire is to run it at 400Hz for a little while. Don't ask how I know that.

Neon sign transformers are also rather dangerous to play with... be warned.

I'm quite aware of the dangers and how to avoid them, what about using a simple function generator after wards to modulate the frequency. I just want a high voltage ac that I can modulate the frequency of.

berkeman
Mentor
I'm quite aware of the dangers and how to avoid them, what about using a simple function generator after wards to modulate the frequency. I just want a high voltage ac that I can modulate the frequency of.
Well, you will need to build a transformer that has a wider frequency range than traditional 60 Hz transformers. You should use more like an audio frequency transformer construction, with a large enough turns ratio to give you the high voltage that you seek.

Keep in mind that you will need a more powerful source than a 50 Ohm signal generator to drive this transformer, however. Assuming not much loss in the transformer, the power you drive in has to equal the power out.

Have you wound any transformers in the past? Depending on the core configuration, it may not be too hard to wind one up, although having access to a coil winding machine is a big plus.

I did a quick google search on audio transformer winding, and got some good hits. This one is a jem:

http://www.jensentransformers.com/an/Audio%20Transformers%20Chapter.pdf [Broken]

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How about just modulating a flyback transformer pulled from an old TV or computer monitor?

These things operate in 20 KHz frequency range.

Thanks for posting the link Berkeman, very useful info.

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stewartcs