Start asking most 11 meter amp builders questions like how do you handle negative screen current, what impeadance transformation and Q is appropriate for the grid input circuit, how to regulate the screen and bias supplies, or how to safely neutralize a large tetrode and you get that "duhhhh" look! Sure the tetrode has significant advantages over the triode in terms of gain and reduced drive power. The number of large broadcast tetrodes properly working on this band can probably be counted on your fingers.
Simple protection of any grid can be done without significant added cost. All it requires is the use of inexpensive opto-couplers that interrupt your keying relay and are triggered off existing meter shunt resistors. Ameritron has grid protection with an add on board for $30 that could be adapted for screen grid use on a tetrode.
Those pesky screen bypass caps blowing up just when the amp starts making good output has plagued tetrode builders for years. This is a big tetrodes way of insisting you build it a shunt regulator for it's screen grid. It's all about secondary emissions and negative screen current that wants to drive the screen voltage up towards the anode voltage through this second current path within the tube. Strict control over the screen voltage is the way to get the tetrode linear to "take off" without a bang.
No matter how well you design a tetrode amp it almost always requires neutralization because of the high gain. This has to do with the inter-element capacitances within the tube that tends to couple the input stages to the output stages, causing the amplifier to oscillate. Neutralization cancels this problem by taking a small sample of the output, feeding it through a cap or coil to invert it's phase 180 degrees and applying this signal back to the input.
