[Boatanchors] E.F Johnson calibrator 250-28 tube?

[Bruce Ussery]

I recently brought an HQ-140-XA back to life. The more I play with it the more I like it's smooth, accurate tuning and good audio. A previous owner added a 100 kc crystal calibrator (and did a neat job), but it's not the XC-100 model that is mentioned in the manual. It's an E. F. Johnson 250-28 which looks pretty similar. It's working OK, but the tube number is scraped off. If it croaks (probably not in my lifetime), I don't know what to replace it with. My usual searches revealed to details of this unit, only that it exists is other hams shacks. So-- does anyone have one or know what the tube is? I promise to add a nice label for the next owner.

Bruce
WA4ZLK