I need help to decide what components can cause the broiler flames to
turn off after running for 10- to 15 minutes.

Which components are possibly bad is my question?
Robert Shaw thermostat
Pilot's thermocouple
Big Saftey valve with red pushbutton in back of stove
Something else?

Symptoms
----------
Pilot for Broiler is always on
Turn on Broiler and set to 350F
Broiler lights and has flames from all holes
Broiler runs OK for 10 to 15 minutes at 350F
There is a LOUD KLUNK sound from rear of stove.
Broiler flames are all gone.
Pilot is still lighted and visible..blue flame..yellow tip
Turn Broiler knob to OFF
Push and release RED knob on safety valve in back of stove.
Turn Broiler knob back to 350F
Broiler relights and is full of flames again
Let Broiler run and it will turn off by itself again.

Why does the large Safety valve in back of stove stop passing gas when
pilot is still lighted? Why must I reset the safety valve to restored
gas flow?
How can I fix this?

ThanksDave_S