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6.
Disconnect the 4-ohm resistive load from the
amplifier, but do not disconnect the distor-
tion analyzer.
7. Adjust the generator output level until clip-
ping occurs. See Figure 10.
8. Verify that the display is free of parasitic
oscillations. If parasitics appear, under this
no-load test condition, refer to Trouble An-
alysis section.
CAUTION
Do not perform short circuit test if
amplifier shows any signs of para·
sitic oscillation.
9. Connect a short circuit across the amplifier
LOUDSPEAKER terminals for' about 10 sec-
onds. The overload indicator lamps should
light very brightly until the short circuit is
removed.
OUTPUT TRIMMING PROCEDURE
1. Set up test equipment and amplifier as in Har-
monic Distortion test (paragraph F), steps 1 thru 4.
2. If amplifier starts to clip before 17.32 volts (75
watts) decrease the value of R28 or R36 by shunting
with another resistor. The proper value may be de-
termined by connecting the trim box (figure 1) across
R28 or R36 and selecting the value that will permit
the amplifier to clip symmetrically between 17.32
and 18 volts (75 to 80 watts).
3. In some cases it may be necessary to use two
resistors in parallel in order to obtain proper clipping
point voltage.
4. If it is not possible to obtain a high enough
clipping point voltage with the above method, it will
be necessary to try substitution of the output, driver,
or regulator transistors.
5. If clipping occurs at a point above 18 volts (80
watts), the value of resistor R28 or R36 should be
increased.
6. To increase the value of R28 or R36, remove
the black jumper wire connecting one end of the
resistor to the socket contact of output transistor
Qll0 or Q113 (DTM-13 or DTM-14) and substitute
a suitable length of resistance wire. Use of 24 gauge,
1/4-ohm per foot wire (approximate requirements)
will result in convenient lengths.
7. The length of the resistance wire required must
be determined empirically.
8. If the clipping point voltage still remains high,
substitute the output, driver, or regulator transistors.
7
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