K4005 - optional sensor for thermal protection

Thanx a lot for former advice with the volume pot! But I have an another issue that I need to help with…

Because of limited possibilities of our reseller, I can not order the optional component used as sensor for thermal protection and I have to replace it with some OEM part…

But I really do not know WHAT type of component it is? I could not find any closer information in the manual. The only thing I guess - it should change its resistance at a given temperature sharply to zero, and to tell you the truth, I absolutely have no idea about it… Thermistor is much more linear… Some bimetallic switch?

Thank you again in advance for any information!

Be assured, there is really no need for this sensor. Only if you are going to use the amp at max. level for a long time in very bad conditions, then there is a need for this part. It is a normal open thermostat that closes at 95°C.