Now that I have my Sparton up and running, thought about tossing the idea in of adding surge protection. Does anyone here know what size thermosistor to put in line for one of these radios? I have never really used them in any practical applications. But thought it would be a good idea as well as a fuse. Such an inexpensive item to prolong the life of the radio. Any ideas, I'm all ears. Thanks.

Here is a link telling about the use of a CL-90 thermistor.

http://users.netonecom.net/~swordman/Radio/TubeSaver.htm

"A CL-90 thermistor from Keystone Thermometrics. It looks like a black disk ceramic capacitor about an inch in diameter. But it acts as a variable resistor. At room temperature, its resistance is 120 ohms. Connected to 120 volts, that means a maximum of one amp would flow through it. As current flows through, the resistor naturally heats up. As it gets warmer, its resistance gets lower. That's the NTC characteristic. The CL-90's maximum steady-state current rating is 2 amps. At that current it heats up until its resistance drops to about 1.18 ohms. The Type CL Thermistor Spec Sheet from Keystone gives these resistance values for the CL-90"