The photo to the right shows all resistors soldered in place. You are done with the resistors (and frankly the most tedious portion of this build). 4 Resistors R14 and R15 are slightly larger 1 Watt resistors. Insert, solder and trim R1 through R13 as well as R16 and R17 (R16 and R17 are 1% resistors). 3 Resistors R1 through R13 and R16, R17 are 1/2 Watt resistors. Bend it to fit in the two holes labeled J and solder and trim excess. Make this jumper wire by stripping about 2 inches of insulation from the same 20 or 22 gauge solid copper wire you used for the filament wiring. There is a single jumper wire that connects two portions of the ground plane (on the bottom side of the PCB). The photo to the right shows the completed filament wiring.ģ 2 Flip the board over weʼre done for now with the bottom side of the board. Insert and solder the last twisted pair of wires as you did before. The last pair of wires runs from where the second pair ended to a pair of holes near the edge of the board (see photo below). Prepare the ends of your twisted wire as you did before and solder as before. They go to a similar pair of holes underneath the last tube. The second pair or wires start where the first pair ended. Cut the twisted wires to an appropriate length, strip the ends and solder. The twisted wires should attach to the PCB at right angles and form sort of raised bridges (the photos show this somewhat). To reduce the introduction of AC hum into the amp, often builders will raise the twisted heater wires up off the board keeping them away from the PCB. Run the twisted wire across to the closest pair of holes in the center of the center tube. Solder the two wires on this end to the two small holes in the center of the first tube (see photo to right and photo at bottom of page). With your long twisted wire untwist 1/2 or so from one end and strip back about 1/4 of the insulation. We will be inserting these from the bottom side of the board and soldering them on the top side! See photos. If you twist them too tightly you are in danger of breaking the wires, so donʼt get carried away with the drill. The photo on the right shows a portion of the twisted wires. Take two 12 inch pieces of 20 or 22 gauge solid copper hook-up wire and twist together.
Three twisted pairs of wires will make a sort of daisy chain connecting each of the vacuum tubes and finally ending at a pair of solder pads on the far edge of the circuit board.
2 Firefly PCB Assembly 1 The filaments of each tube are wired with a pair of twisted wires on the bottom side of the circuit board.