Can a 5z4 tube be a metal bottle?

I did a thread on some tubes unfamiliar to me and recieved great info. The 5z4 rectifier seems to come in a metal and glass bottle from what I have seen thus far. I also wanted to know if the GZ30 tube would sub for the 5Z4. As always enjoy the music.
Rodman9999 again you come through. I have some tubes I saw on another site that I might try. One is a GE the other a RCA. The pre should be here next week. Stay tuned.
Ah the famous Mullard. I have a pair in my current pre (6922,6dj8). Very nice indeed. How common are the Mullard 5Z4 tubes Rodman99999?
People generally lump all the 5Z4, 5Z4G, 5Z4GT tubes together with the equivalent replacements (the CVs/GZ30). Mullard drop in equivalents are common:( ( ( (