This is a nice testing early French type 5Y3GB or U50 vacuum tube made by RT or La Radiotechnique.  It appears to have a 1955 date code and has the RT factory mark on the glass.  It tests strong on an AVO tester for plate current.  The only issue is there is a hairline crack on the base.  This does not affect operation and the glass is tight.  Satisfaction guaranteed.  The sale is for the item shown here.

TERMS OF SALE: Serious bidders only, please.  Payment is expected within 3 days of auction close.  We ship by first class mail to the name and address of the winning bidder provided to us by PayPal and/or eBay.  Free domestic shipping in the USA.  Outside the USA use the eBay calculator to figure shipping cost.   We declare the full value on the customs forms for any international shipments.  International bidders should be aware that first class mail cannot be tracked and that processing delays up to several weeks can occur in customs, which is beyond our control.