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- Cosmic Ampworks
6. Installing new components (wear safety goggles!)
1.
Solder a 1M grid leak resistor across the connections of the input jack (Figure 8).
Figure 8. A grid leak resistor keeps the grid of triode 1 at DC ground potential, so that the correct bias is maintained.
2. Mount (solder) two 1.5k resistors in place of R2 and R6 (Figure 9).
R2
(Heater wire)
Figure 9. Two 1.5k resistors are to be installed in place of R2 and R6, setting the bias of the first preamp tube to a more normal value
than the stock GA15, which is biased very cold). For now, ignore Wires 1,2 and 3 – these connect to the gain pot (see point 4 in this
section, p.11). Also ignore the white, rerouted heater wire (see point 6, p.16).
3. Solder a 22uF electrolytic capacitor in the spot of C4. Electrolytic caps have a positive and a negative side,
so make sure to insert the negative pin (indicated on the capacitor label) on the side of the vertical dash in
the little round symbol on the circuit board (Figure 10).
© 2020 -
www.cosmicampworks.com
- The Ultimate Harley Benton GA15 Mod Kit- Version 1.4 - 200127
®
Wire 1: Signal
from anode of
triode 1 (via C2)
10
Wire 2: Signal to
grid of triode 2
R6
Dedicated to the Advancement of Stellar Tone!
Wire 3: to
ground
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