OSVTTC – The Tube By davek0974 | 01/07/2005 - 2:02 pm |11/04/2015 Oscillator Driven Vacuum Tube Tesla Coil, Tesla Coiling The GU-81M Tube. The picture is deceiving, it measures 260mm tall and weighs in at 1kg ! It’s original use was for Russian military radio transmitters, 700w of pure high frequency electrical mayhem ! It’s the same unit I used in my first VTTC. GU81m Bookmark the permalink.