The Mesa website has it as a EL34/6CA7 tube. Does this mean all Svetlana EL34 tubes are this or just Mesas? I know Mesa does not make tubes . Are there different makes of Svetlana EL34 tubes? like regular EL34 SED or just the kind Mesa sells (EL34/6CA7) I hear the 6CA7 tube is a cross between the EL34 & 6L6. Just wondering if there are differences in Svetlanas?