An accurate and up-to-date NDB listing can be found at http://worldaerodata.com/ My web site at http://www.computerpro.com/~lyle has a number of LowFER construction projects. Everything there is solid state -- I haven't messed with tube stuff for many years, and would probably electrocute myself if more than 24 volts were present in a circuit. Lyle, K0LR