depth charge 4004 amp problem

I have never seen a depth charge amplifier so I will be no help in getting it apart.  I need you to remove the bottom plate so you can see the circuit board.  You then need to identify the amplifier section of the amp.  Chances are it will be the end nearest the RCA jacks.  There should be 4 identical looking sections.  The larger transistors that are mounted to the heat sink are the output transistors.  I need to know what kind of clamping mechanism they are held to the heat sink with.  Screws and metal bars, spring clamps with a square hole in the middle of them?  Set your meter to the diode test function.  This is the symbol for a diode

There are going to be 8 output transistors.  Place the black meter lead to the center leg of a transistor and place the red lead to one of the other legs of the same transistor.  Notice the reading.  Then place the red lead to the other leg of the same transistor, notice the reading.  Repeat this for all 8 transistors. One set of them will give you a much lower reading than the others.  Let me know what you find out.