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.
Look like my question went on deaf ears. However I did find two pics of 5Z4 tubes that are in a metal case. Quite different from the glass tubes I'm used to seeing. Now if I can find the subs to these tubes it would give me some other choices.
I tried to respond yesterday, but my post didn't make it. YES- the 5Z4/CV1864 was manufactured with a metal envelope as well as glass. The CV1863 and CV2748/CZ30 were both designed to power up to 40 watts as well, and will replace it.
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.