Universal Cartridges in the 1950-60's sense does not mean the same as Universal or International does today. Esterbrook cartridge pens can only take their own proprietary cartridges, but sometimes modern cartridges will fit and work. Sheaffer works on some model, provided you puncture the seal before trying to insert it. Lamy also works on some, but is slightly loose, so maybe not the best bet. Platinum converters do fit on some of the other pens (Phaeton 300 I believe) so it all depends on what you might have lying around you can try. If you like the pen, keep it, it's not impossible to find something to make it work, or to try and find an original cartridge.