It's not just the high voltage, the geometry difference between the round tube and the rectangular would prevent it from displaying a picture correctly.

The rectangular tube will work in a round set but it's useless for setting it up.

Edit: Phil beat me to it by two minutes!

Yes, I would imagine that it is simply for someone like me trying to check voltages on one of these non chassis mount crt sets. You would just need to see the basics as far as sweep, brightness, sync, etc. Definitly no way to set up picture...

Here's what they look like side by side. Left to right we have the 8YP4, 8XP4 and 5AXP4.
http://farm6.static.flickr.com/5122/...2de0c3ae_z.jpg

Rauland Box
 

Bob,
Boy, that Rauland box sure triggered a lot of old memories lost up there in my cranial cobwebs.

Wow! That on the left is interesting. A lot of my vintage test equipment and NRI stuff came from a pile of stuff that a friend found on the curb after an old repairman died and his wife decided to sweep his memories to the dump. Anyway, out of all of the stuff that I did get, I DIDN'T get a bunch of maybe 4" round crts with a grid of some sort on the face. The socket and neck seemed to be the same size as any 40s-50s tube. I thought that they would just be more useless stuff taking up space, but now I wonder if some museum might be interested in them. They are still there as far as I know. The one in your picture looks like the neck is much smaller than the others.

I was very happy to get the original box and paperwork. I didn't look like it had ever been used.

I've seen a number of 8YP4s with a grid on them. Mine uses a tight fitting plastic film with the GE logo in one corner.
Yes, the neck is the smaller type used on newer, more rounded B&W CRTs.

http://farm6.static.flickr.com/5247/...d5eb7cea_z.jpg