A and T Labs
K6 Audio Power Amplifier Assembly Manual
2001 A and T Labs Inc.
AMK6a
15
noticeable heavy AC power line load, as evidenced by flickering lights), check for
short circuits in the output portions of the power supply. This could include, for
example, output capacitors shorted or installed backwards, or rectifiers shorted to
the heat sink.
4.3 AMPLIFIER TESTING
The amplifiers will first be tested without the output transistors installed. Begin again by
carefully checking that all components are present, the correct value or type, and
properly oriented. A little bit of patience and scrupulous inspection at this point can go
a long way in avoiding smoke, loss of expensive parts, and endless troubleshooting
and heartache later!
At this time, install the heat sink adapter L-bracket, drilled and prepared previously,
with the temperature sensor TC1, (Our kits come with one over temp. cutout per
channel. Mount it on the forward end of the board where the LEDs are, opposite the
input jacks. See figures 9 and 10). Install temperature sense FET Q24, and regulators
REG1 and REG2. Use transistor insulators, heat sink grease, and do not over tighten.
4.3.1 Amplifier Miscellaneous Power Parts
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Part
Description
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Part
Description
REG1 LM317T
TC1
67F080
REG2 LM337T
Q24
IRF510
Install 1/2 amp fuses for F1 and F2, and temporarily connect the power supply to an
amplifier board, making sure all power polarities are correct. These tests can be
accomplished by carefully laying the modules out on the bench. Be sure they are all on
insulating surfaces! For these tests you may wish to use the current limiting capabilities
of the power supply for extra protection. This can be achieved by placing a jumper on
the power supply board between the junction of R17 and R18, and the junction of D5
and D9. Apply power and check for the +/- 15 volt supplies on the board and the +/- 30
volts at the input stages. Do all probing very carefully, as a slip with a probe can easily
result in a damaging short circuit!
Very carefully measure the voltages across D7 and D8. They should each be in the
range of 3 to 5 volts. Adjust R18 until they are each less than or equal to 3.5 volts. If
you have a signal generator and oscilloscope, an additional valuable test is to apply a
very low level signal, say 5-10 millivolts at 1Khz, and check for drive signals at the
emitters of Q14 and Q15. Since the amplifier is open loop at this point, the drive signals
will easily overload, and look like square waves, about 12 volts p-p or less, as limited
by D7 and D8.
