Does anyone know what type of tube is the one on the back left corner? It has that unusual looking cap. When you take that plastic/metal cap off, it looks like the one in the back in the bottom photo.
For good measure, feel free to identify the type of other tubes. I'm still very new to tube but am looking to learn as much.
The model of the amp is F50 and I thought it referred to the tube but I can't find it on the web.


Thanks,
UL