Rectifier for B&K 350 CRT Tester?
 

Saw this beast in a corner but I can't find any documentation of what tube goes in it. It's the smallest of the 7 pin sockets.

Most common 7 pin rectifier tube I can think of would be a 6X4. How does the wiring compare with a 6X4 pinout?

That’s it!

Thanks so much for the information. I don't know how much this differs from the more common 400 but I work on a lot of 1948-1950 TVs and this seems like a neat novelty to have on the shelf at least for CRT quality determinations. Not sure I want to rejuvenate a 10BP4 with it!

If it's anything like my 400 the rejuvinate is pretty brutal. The trick is to hit the button as fast as you can and watch the emission come up. I've used it a few times in situations where there was little to nothing to lose and actually had decent results.