A heat source assembly for use in adhesively joining together thermosetting resin impregnated members. A heat source consisting of a combustible material is enclosed in a non-combustible insulation which moderates the flow of heat to the joint area and also prevents rapid cooling to maintain uniform heating temperatures. The aforementioned abstract is neither intended to define the invention of the application which, of course, is measured by the claims, nor is it intended to be limiting as to the scope of the invention in any way.