Hi nobie1,

-Make sure all your solder connections are not cold solder joints. Look this up on you tube if you don't know the proper way to solder and what a good joint should look like.
-Make sure the metal faces of the transistors are not touching each other and making electrical contact... If they are mounted on the same piece of metal, you will need transistor isolators that go under each metal face before it is mounted.
-You should not need transistor paste, next to no heat will be generated if you run the machine the way it was designed. 7 strands = 875mA, primary draw. If you push the machine beyond one amp things will heat up... heat = waste of energy, not good for conservation.
-Double check all connections to ensure proper wiring according to schematic.
-Check the condition of transistors... as they can get damaged if you short out certain wires while assembling. Always carry extras on hand if you like to experiment.

Hope this helps.

Dave Wing