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e. Attach the L7912 to the heatsink with the little nut and bolt that are included and put some thermal
grease on their contact surface.
f.
Run the wires that you soldered to the L7912 through hole 1 (Figures 19 and 20) and solder them to
the correct (doublecheck!) holes in the component's original place (Figure 18).
g. Attach the heatsink and voltage regulator assembly to the chassis with the tie wraps. Don't worry
about the combination of plastic and heat; the heatsink has such a large capacity that its
temperature will not noticeably increase. It might be a good idea to stick some pieces of
gaffer/duct tape to the underside of the chassis surface where it will be in contact with the
heatsink, for some extra protection/stability.
Figure 18. Carefully remove the L7912 voltage controller (empty space encircled) by de-soldering it, NOT by clipping its legs
(encircled area in Figure 20 shows protruding ends of wires that are soldered underneath the board, not clipped component
legs). Make sure not to heat the L7912's legs for too long, or the sensitive component may be damaged.
h. Drill two holes (best from the underside of the board) near the second preamp tube (second tube
from the left of the chassis - V3 in the schematic):
i. Drill hole 1 right next to the tube socket solder connections for pins 4 and 5 (Figures 21 and
22); the location is not particularly critical.
ii. Interrupt the circuit board trace running to and from pins 4 and 5, on both sides (Figure 21).
Use a file, rotary drill or Dremel tool, for instance.
iii. Drill hole 2 just above the tube socket solder connection for pin 9 (Figures 21 and 22).
Make sure not to accidentally damage the wire bridge on top of the board. Ideally, also
interrupt the circuit board trace in go, because the heater traces spread hum throughout
the circuit in their stock layout.
i.
Drill two holes near the first preamp tube (leftmost tube, seen from the front of the chassis - V2 in
the schematic), much similar to the holes drilled near V3 (see f.):
i. Drill hole 3 right next to the tube socket solder connections of pins 4 and 5 (Figures 23 and
24); the location is not particularly critical, but make sure not to damage the trace running
from pin 6 of the tube (anode) to R7 (load resistor).
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- The Ultimate Harley Benton GA15 Mod Kit- Version 1.4 - 200127
®
Heater wire
17
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