1 Penta Labs 4D21 aka 4-125A Vacuum Tube. The 4-125A (aka 4D21) is a transmitting VHF beam tetrode tube. 125 -Watt Transmitting Tetrode. There is Uranium glass where the pins exit the tube – top and bottom – see photos.
1 Penta Labs 4D21 aka 4-125A Vacuum Tube. The 4-125A (aka 4D21) is a transmitting VHF beam tetrode tube. 125 -Watt Transmitting Tetrode. There is Uranium glass where the pins exit the tube – top and bottom – see photos.