Hi, I'm testing some 5071A units and have come across a unit that has a tube S/N US38390709 . When I run the profiling software and the status screen comes up it lists the tube type as "non-standard". The other units that have a normal looking serial number (3124A00132 or 3128A00532) come up with tube types of 10890A and 10891A respectively. The measured performance of the US prefix tube indicates a standard tube performance as far as short term stability goes. Anyone have any idea what specs would be different on this tube, or what application is was built for? Thanks! Corby Dawson ____________________________________________________________ Click now to find great remedies for hangovers! http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTKyJrBgCfaJwe0CjuqO66SQ7GWPrXNbZAgVNM13qxWoHN2lvZRYh6/

Corby, I think the S/N format you're showing was adopted sometime in 1996. If this is correct, then your USxxxxxx tube is a bit newer than the rest. See, http://www.hpmuseum.org/collect.htm#numbers Pete Rawson