Current Limiting Bulb replacement for VTVM

Hi all,

I’m currently in the process of restoring a Grundig RV-3 VTVM from 1961 (schematics can be found here). I should start out by saying that this is my first more complex restoration project, so there’s tons I still don’t really know and need to learn.

One of the things I stubled over are R43 and R44 (lower right in the schematics), labeled EW 3-9V 0.3A and EW 7-21V 0.3A, which appear to be current limiting bulbs for the heater filaments of the tubes. While they still work at the moment, they’re bound to break at some point. Googling a bit, I’ve seen that the filament appears to be made of uranium dioxide (the wonders of the atomic age!), so finding an exact replacement is bound to be very unlikely nowadays.

Looking around for bulbs with similar specs that would also fit with the bayonet mount used left me empty handed, so I’m wondering what I can use as a replacement when the time comes. I’m guessing some NTC, but what dimensioning/specs should I look for there?

Thanks a bunch,

Sven