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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