Very good again!

Now can you see it better.   Read on the tube socket.
This is the Sovtek OC3,  105 Volt Voltage regulator tube!

This tube is heated: Indirectly - Directly
It has no filament at all.  True - Not true

Feautures:
It is more precise than a Zener Diode.
They can be serialized to get 210V, 315V, 420V, etc.

The price?   Check  here