[Fred27]

My Chinese eBay laser (DC-K40IV) is working well - after the usual "maintenance" like putting the bits that had fallen off back on again. However I noticed yesterday that the ballast resistor has a nice purple arc across it about 1cm in length. It was arcing to the case but when I moved it it continued to arc between two points on the resistor. I'll take a photo when I get a chance.

Does anyone know what would be a suitable replacement? I was thinking maybe this (50W 50KOhm 1.25kV) would do. The voltage seems a little low but I can't find anything higher. I assume that heatsinking wouldn't be an issue as the current one is just wrapped in electrical tape and cardboard.
THS5050KJ - TE CONNECTIVITY / CGS - RESISTOR, AL CLAD, 50W 50K 5% | Farnell United Kingdom

Also, would using it a little in the meantime be likely to damage the tube?

[Frogblender]

Did you find a resistor? My original resistor has also started throwing off sparks, and I'm having trouble finding a replacement with a 20kV voltage rating.

[Fred27]

I went for the one linked above and it worked perfectly. Seems like much better quality compared to the original. I don't think it takes the full 20kV as it's on the return side. Anyway, it works.

Sent from my Nexus 5 using Tapatalk

[Cromaglious]

replacement ballast resistors for K40 laser

I've found these:

2.8kv 100w 50k ohm for $12 ish L100J50KE - Buy OHMITE L100J50KE Online at Newark element14

1.6kv 50w one for $14 ish L50J50K - Buy OHMITE L50J50K Online at Newark element14