Heathkit SB-1000 - Periodic Maintenance

Page 64
adjust the LOAD and PLATE controls for
maximum output on the 0 to 2000 scale.
10. Increase the exciter drive until you obtain 125
mA of grid current. Now readjust the LOAD and
PLATE controls for maximum output. The grid
current should decrease.
11. Increase the exciter drive for 200 mA of grid
current. Then readjust the LOAD and PLATE
controls for maximum output power (repeat this
step twice). The output should now be around
1000 watts with 100 watts of exciter power.
12. Apply only enough drive to indicate either
1000 watts of output power, or 200 mA of grid
current. Then repeak the LOAD and PLATE
controls. NOTE: The grid current, plate current,
and output power must not exceed the following
limits:
Grid current ——___ 200 mA 5
550 mA
1000 watts
Plate current
Output power
13, When you operate in CW, reduce the drive
power until the plate current is 400 mA or less.
‘The Amplifier is now fully loaded for operation on
CW. If you desire to reduce the Amplifier output
power, refer to Pictorial 10-3 for the plate voltage
and current indications that will produce various
DC power input levels. If you use an oscilloscope for
monitoring, you should obtain a display similar to
that shown in Pictorial 10-4. If you have a monitor
scope, you may find that you can more readily
Heathkit
interpret voice pattcrns on its optional trapezoid
display.
SSB PROCEDURE
1. Tune up the exciter and Amplifier as described
for CW operation. NOTE: In the absence of the
recommended oscilloscope monitor, either the
Plate Current or the Output Power indications
may be used to monitor SSB transmissions.The
Plate Current indi-cations are easicr to follow.
2. Advance the exciter drive and audio levels so
that the modulation crest does not exceed 400
mA of plate current, 100 mA grid current, or 1200
watts PEP out-put.
An example of a proper SSB oscilloscope pattern is
shown in Pictorial 10-5. Note that there are sharp,
distinct peaks. The number of patterns or "christmas
trees” depend upon the operator's voice character-
istics and the scope sweep speed. Set the scope for
approximately 30 Hz sweep.
Note that the meter indication on voice peaks is not
high, due to meter inertia and voice characteristics.
The height of the oscilloscope pattern, however, is
greater than that shown in Pictorial 10-4.
Pictorial 10-6 shows the same voice pattern, but
with extreme "flat-topping.” The oscilloscope shows
that no more useful power is being developed. When
the drive level is too high, the meter indicates
higher, but only distortion is developed.
PERIODIC MAINTENANCE
Remove the top cover from the Amplifier at least
once a year and remove the dust. Dust accumulation
can help cause the variable capacitors to arc between
plates. Use the blower connection on a vacuum
cleaner or a soft bristle brush. While the top cover is
removed, add one drop of light machine oil to each
fan bearing.