CRT and yoke question
 

Has anybody ever used a small neck B&W CRT on a large yoke? I would imagine there would have to be a spacer added so it would be stable.

Experimented with that once and it way overscanned, used tissue paper tubes to sorta locate it in the middle

Yes it can be done, but not very well.
I used a 8YP4. Test Picture Tube to restore my FADA 895, (RCA 630TC) clone, it worked well enough for repair till I changed to the 12LP4.

Think my mistake was using a 110 degree yoke on a 12CNP4... was in the 5th grade at the time.

Generally when you use an old narrow deflection TV with a newer wide deflection test CRT you will end up with cropped underscan...The yoke won't be able to bend the beam to the edges and neck shadow will crop it down to a ~5" circle in the center of the CRT.
Doing it the other way around 40s test tube in a 60s fat neck set will have obscene overscan.
Either way it's fine for assessing signal chain and sync function and finding gross sweep issues, but it may hide more subtle sweep problems until switching back to the correct stuff.

Don't remember all the details other than they were both panasonic sets that looked the same. Spliced the CRT wires to the small socket, got the S#!* shocked out of me from the anode cap and tried to center the yoke with some tissue paper tubes & masking tape... this was around 1980

Thanks guys. The reason I asked is that I found a B&K1077 on Ebay but it has no CRT. So I think I can get it for $5 (plus shipping).
https://www.ebay.com/itm/18646549509...3ABFBM-LLCpKVl
Here's where I come in. I have an unknown tube that I think will work. Its a Motorola tube that I think is a flying spot scanner tube. I connected it up once and it glowed purple. I think its either military or medical. Has an attached HV lead.

I have an identical Motorola tube (no clue what it's from) base, neck diameter and screen size are wrong for the B&K...You might be able to make it work, but I wouldn't expect great results.

I think the deflection angle is the same- 90 degrees. The neck diameter is smaller so it would need the toilet tissue tube spacers. I can make some smaller slides. I've got a Pomona adapter to adapt the base.

Yeah, I've tried it before. You definitely need some kind of spacer or shim to keep it stable, especially with the larger yoke. Without it, the neck can wobble or be misaligned, which messes with the picture. Just make sure whatever you use to secure it doesn't interfere with the electrical connections or airflow around the tube.

What is the face diameter of this tube?

3.5 ".
There is one on ebay:
https://www.ebay.com/itm/16302824739...Bk9SR8Kcvq6mZQ

It is likely a flying spot tube from the ill-fated EVR Player. Motorola developed a fine-grain phosphor for it ca. 1970-1972.
It amazes me that any still exist.

http://www.bretl.com/EVRdocuments.htm

That brings back memories. I acquired several EVR players when they were being sold off for next to nothing. I made quite a good monochrome flying spot slide scanner.

I just remembered - the EVR tube was magnetically focused, and also used beam alignment magnets. This was done to get an extremely fine, but still bright, spot.
So if this is an EVR tube, I'm afraid it won't work without those parts/circuits.