This is somewhat off subject, but since I'm using my HP410B to troubleshoot my XB50, thought I would ask. I'm trying to find the tip and contact spring for the 2-01C tube in a HP 410B RF voltmeter. Part #410B-21N. I did a web search, but no luck. Anyone know a source for these older HP parts? Tnx #3481 N2tK, Tony