Solid State relays or Mechanical relays in a heat treating oven

The solid state relays take the place of the mechanical relays that can wear out over time. It's a good idea to get the solid state relays if you're going to be heat treating stainless steel or plan on tempering in your kiln. Also, the solid state relays will hold the temperature within a tighter range than mechanical relays. The mechanical relays are set to hold a temperature within about 25 degrees Fahrenheit. This is an attempt to make the mechanical relays last longer when they're holding a temperature.  I chose not to get the solid state relays with my Air Bath because I don't really do any 'hold times' with the simple steels that I use (unless I'm using 80CRV2 and I use a 5 minute hold). But now I wish I would have gone ahead and gotten the solid state relays because I could temper in the kiln easier and I could make my wife some stainless kitchen knives.