What do you mean? Triphosphor tubes are the only kind you can buy right now.

An Ov-50? That’s a good find!

I second Tim. Definitely try it locally if possible—such as OfferUp, Craigslist, Marketplace. I’ve seen an OV-50 pop up in my region way back when doing that.

I don't know if they ship to Finland. All of these are with offers. Last one is very nicely priced. You will need the Philips SX76 ignitor.
https://www.ebay.co.uk/itm/326535770415
https://www.ebay.co.uk/itm/315185634080
https://www.ebay.co.uk/itm/396669150993

Very interesting, I wonder where the barium comes from. Good to know it isn't just tungsten from the cathodes

I did a bit of research, and it turns out it is not a getter; it is excess Barium that evaporates at some stage in the arc tube filling process. Everything else I said is correct though.

There is a getter in the arc tube?!?! This is news to me! What is it made of?

Here's what I have heard. In the factories for SOX lamps, they used a sensor of sorts in order to ensure that the getter applied inside the arc tube was even on each side of arc-tube. In later years, this sensor ended up breaking, the result was uneven coating of the getter inside the arc tube, often with one electrode getting an absolute sock while the other only got a small amount.

A glow bottle fluorescent starter won't strike a 90w, believe me. Yes they do work for 10-18w (18w is a bit hit and miss). I haven't personally tried on a 35w but can confirm it doesn't work for a 55w. Therefore a 90w definitely won't.

Just buy a 90w ignitor, they're on eBay. They're a Philips SX76. Don't risk such expensive lamps on the wrong equipment.

@Ash
Yes of course, absolutely I can use the big equation with ballast impedance to determine PF, that is what I did to determine the average PF values across technologies. These averages are good enough to get ballast characteristics for most more common lamps.

But for other rarer lamps (short arc LPS, linear neon, super high pressure lamps), these averaged technology values are probably far from what the particular lamp actually is. I am sure it would not be wise of me to assume that my NA-1 has the same PF as an average SOX or SOX-E lamp, even though both are under the LPS category they surely are very different. And I am sure linear neon has a PF that is different from fluorescent even though they are physically similar. I don't have ballast specs for these less common types of lamps.

So naturally the need arises to get the power factor of a lamp which you don't have the ballast specs for, so you can use that PF to calculate the ballast specs. Let's use a 160W NE/H for example. I know that a 160W NE/H runs at 157V at 1.33A, but cannot find ballast specs for it. I normally should be able to calculate PF with just power, voltage, and current (PF=W/VA), but we have just proven that for some mysterious reason that method doesn't work accurately for discharge lamps (that calculated power factor does have applications that I have found, just not relevant here). Dead end.

So I can't get PF because I don't have ballast characteristics, and I can't get ballast characteristics because I don't have PF. Is this a standstill? Is there anything we can do for situations like the NA-1 or NE/H to get either PF or ballast characteristics from jus tthe running specifications so we can solve the puzzle?