What to use to power an X-ray tube filament - Page 1
Forum section: electronics / projects

author: Neukyhm
author_rank: Contributor
timestamp: July 24, 2018, 03:27:38 pm
content: Hi everyone, I need to power the filament of an x-ray tube. I was planning to use a simple step-down converter bought on eBay and a relayThe filament (cathode) is grounded btw.Maybe it's not the best option to avoid the filament from breaking, for example, maybe it's better to power the filament slowly than using a relay to power it fast.

author: In Vacuo Veritas
author_rank: Frequent Contributor
timestamp: July 24, 2018, 03:33:04 pm
content: Are you sure you "need" to, orwantto?Guys, I need to launch a missile, I was planning on simply filling a pipe with gasoline bought at the gas station.The pipe is pointy at one end, and open at the other (the flame end).

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 24, 2018, 03:56:28 pm
content: You didn't mention any specific factors like voltage and current? Is this something with a higher voltage filament (implying more fragile heater wires), or is it a low-voltage, high-current element (implying more beefy current path). I would think that a higher-current, lower-voltage heater would be less vulnerable to switch-on current surge. How are tubes like that powered in the original equipment? Do they have soft turn-on?I was just watching a YT video about 500KW broadcast transmitter where they had output tubes with 3-phase heaters. And before that they had motor-generators as big as your car to crank out amazing amounts of DC current to heat up the output tubes.

author: In Vacuo Veritas
author_rank: Frequent Contributor
timestamp: July 24, 2018, 03:57:51 pm
content: Quote from: Neukyhm on July 24, 2018, 03:34:49 pmI guess not, just point that thing away from me, and have fun explaining your healthy glow in the hospital.

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 24, 2018, 05:07:54 pm
content: It looks like nothing more than a simple regulator circuit. I don't see any large capacitors that might suggest some sort of ramping power function.Note that the filament power board is controlled from the main board so I would expect that it turns on the filament power first and then has a time delay to allow for it to reach proper temperature before turning on the high-voltage generator (which appears to be a simple Cockcroft-Walton voltage multiplier).The diagram shows the filament wiring going through the high-voltage board, but it looks like nothing more than a convenience pass-through. It doesn't look like there is any connection between the high-voltage power supply and the filament wiring. The ground-return current path from the high-voltage supply appears to go through a separate wire.

author: LaserSteve
author_rank: Super Contributor
timestamp: July 24, 2018, 05:47:53 pm
content: Un-doped tungsten cathodes have a small softening /sagging region around 700'C, so usually any soft start slope is designed to be reasonably fast as you get near normal operating range around 1150 C.Big machines have soft start. Obviously this small tube does not.X-rays are very nasty from a safety point of view, watch for backscatter and shield leakage. Be very careful.The only way you know you are safe is to either never power it up, or by making measurements.Steve