WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
As you can see on the tube base is written "036" and "A.25.52" "F8.0". The anodes are big and flat... The base is like on AZ1, but I cant't find similar AZ1 to this...
to be even more specific: I think it is a Tungsram AZ4. The plates are placed really close together, almost in the center of the glass-bulb. I only have seen Tungsram tubes having this structure..
BR
Rob