[Amps] Solid State Relays in Plate Supply Primary

[W7RY]

Since there is nothing in the current archives... What are the pros and cons on using solid state relays for switching on the plate supply transformer of a 1500 watt tube type linear amplifier?

What is the voltage drop across them? I'm going to use two of them, one for applying 240 volts and the other for shorting out the step start resistor. I see that in Jerry's K8RA project in the handbook, he uses four relays instead of two. Any idea why? 

I know that the relays are quiet and provide for immediate shutdown of the HV if an arc occurs but has anyone come into the shack and found the high voltage running on their amplifier because a relay shorted from of a voltage surge on the AC line?

Thanks and 73
Jim W7RY