I have an Aprilaire Humidifer Model 440 that could be fifty years old. The humidistat is not working. On this model The humidistat is a large mechanical slide that is inserted into the side of the cold air return duct. It appears to measure the humidity on a peace of tape connected to springs and a switch. My question is can I replace this unit with a modern electrical type? I have removed a spring in the humidistat unit to trigger the switch to open the valve thus allowing me to manually control the humidity.