A and T Labs K6, Assembly Manual

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A and T Labs K6 Audio Power Amplifier Assembly Manual
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2001 A and T Labs Inc. AMK6a
16
If all is well, you may now mount and solder the output transistors. They must be
matched, and a circuit for matching them is shown in figure 8. (Transistors supplied in
our kits are matched) Mount the transistors on the heat sink angle bracket with mica
washers and liberal silicon grease, and check for absence of shorts between transistors
and the heat sink, then solder to the amp board. For home use and 8 ohm operation,
four output transistors per rail is sufficient. However, if you plan to operate in bridging
mode, or at high power with low impedance loads, include the additional transistor per
rail, for a total of five per rail.
4.3.2 Amplifier Power Transistors
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Part Description
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Part Description
Q16 IRFP9240 Q20 IRFP240
Q17 IRFP9240 Q21 IRFP240
Q18 IRFP9240 Q22 IRFP240
Q19 IRFP9240 Q23 IRFP240
Set the power supply in the +/-58 volt mode. Apply power with a 1 amp fuse installed
for F1, and a milliameter in place of F2. Adjust R18 for an idle current of about 240 mA.
(The bias must be re-set for long term operation at different voltages) Remove the
ammeter and install a 1 amp fuse for F2. Check that the output is within a few millivolts
of ground. Apply an input signal at a low level, and verify that an amplified output
appears.
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Description
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Description
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Description
Idle current set Check output DC offset Signal check
If all is well, replace F1 and F2 with 6 amp fuses, and perform similar tests on the
second channel. If you used it, remove the current limiting jumper on the power supply
board.
5. FINAL ASSEMBLY
Figure 9 shows details of chassis preparation for the packaging shown in Figure 6 for
the 5 ¼” unit. Figure 10 shows details of chassis preparation for the packaging shown in
Figure 7 for the 3 ½” unit. Following construction of the basic chassis, it’s time to mount
switches, connectors, and LEDs, and to install wiring. If you are fabricating your own
case, you will need to drill holes for LEDs, inputs, outputs, power cord, etc. in the
appropriate places. For the 3 ½” unit this includes proper alignment between the front
panel LED holes and the LEDs, as mounted on the amplifier boards.