Because of the simplicity of the design virtually any size round or rectangular or cylindrical cathode may be made, allowing designs for {HEAD ~ direct retrofitting} of {TAIL ~ any existing cathode} 
of
Because of the simplicity of the design virtually any size round or rectangular or cylindrical cathode may be made , allowing designs for { HEAD ~ direct retrofitting } of { TAIL ~ any existing cathode }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL