This is Marconi Triode (pre WWII) I can not identify.
Officine Radio Marconi Genova DES.1 is written on it, also serial numbers and Marconi paper labels
I put them here, because they use the same (jumbo) socket like US 211 VT-4C and German’s RS237. They are also the same size.
Despite asking on many forums and FB it’s still unidentified!
Click to see all 203 211 VT-4C triodes in stock