I don't really care for thick glass version

I think there is a double ended high pressure halogen inside the envelope because this is an old lamp, hence the hard glass. If the halogen tube inside this lamp was a 12V capsule then the lamp had to contain an internal transformer. And if it was a 120V capsule then the pressure was low and the lamp was made using soft glass.

I love those thick glass versions, makes it easier for me to make hand made lamps!

I believe these original Capsylites had 12 volt capsules because they had that characteristic diode flicker. They were very heavy (just like the early GEs too).

I still have several of the heavy GE ones in use around my house.