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.
Guess you'll have to copy and paste that URL if you want to see Tubeworld's offerings.
Wow Rodman99999 nice links. I don't know the current brand of rectifier tube in the pre as of yet but if it's not a Mullard or GE,RCA I mentioned it's outa of there. The OD3 you advised will be ordered shortly. Thanks again : )