This is a "topless" EL509 with quite an other base than the EL509. Svetlana made the EL509-2 for HiFi and was planning to bring out also an EL509-3. October 2011 we received this information from pmcomponents.co.uk: "As far as I am aware, the EL509-III never really made it to general circulation, I believe it was designed for a specific manufacturer, certainly we never stocked this tube (hence my lack of information). The EL509 and EL509-II were both being produced up until about 8 years ago." The tubes are also called EL509II or EL509-II and EL509-III. JJ made an EL509S which is most equal as EL509-2 and a EL509 with this octal base.