You mean a Ceramic/Glass hybrid!!!
Yes, metal involved in tube components.
The origin of the term "Metal Tube" is based on description that comes partially in the discussion of the ANODE Cooling Fins. I always get a kick when I hear/see "Metal Tubes." Those "Metal" fins are removeable in some cases and reused from tube to tube. the Svetlana GS35B/GI7B are good examples.
Not criticizing, I just always found a chuckle when I hear the "Metal Tube" term used in regard to "Higher Power"
Metal jackets used to help cool tubes have been around since 30's. There were several variations where metal jackets or enclosure were used to help cool and protect the interior... 6AG7/6L6 were tubes had metal enclosures in some variations.
OK! I am bored ...I'll move along...Thank You very much 73
Russian power triode GS-35B (ГC-35Б) with maximum anode dissipation of 1,5 kW. These tubes are well known in the DIY world and used in many projects. As you can see from the gallery it has a copper heat sink for forced air cooling.
Heat sink is removable and if you remove it, you will get the GS-35A version of the tube.