Heathkit SB-201 - Troubleshooting Guide

Page 48
Note that the meter reading on voice peaks will not be
high; however, the height of the oscilloscope pattern
is slightly greater than that shown in Pictorial 22.
This increase in peak power is due to dynamic charac-
teristics of the power supply and allows the Linear
Amplifier to develop approximately 20% greater peak
envelope power for a given level of CW input. The
meter will indicate only one-half or less of the single
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PLATE CURRENT
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tone level, depending on the individual’s voice, be-
fore ‘‘flat topping” occurs.
Pictorial 24 shows the same voice pattern but with
extreme “‘flat topping.” The oscilloscope shows that
no more useful power is being developed. The meter
reads higher, but only distortion is developed.
Oscilloscope pattern and plate meter read-
ing resulting from over modulation. The
meter reads higher, but the scope indicates
peak flattening. Operation in this manner
causes distortion and severe interference
to adjacent frequencies.
PICTORIAL 24
IN CASE OF DIFFICULTY
1. Recheck the wiring. Trace each lead in colored
pencil on the Pictorial as it is checked. It is
frequently helpful to have a friend check your
work. Someone who is not familiar with the unit
may notice something consistently overlooked
by the constructor.
2. Itis interesting to note that about 90% of the kits
that are returned for repair, do not function
properly due to poor connections and soldering.
Therefore, many troubles can be eliminated by
reheating all connections to make sure that they
are soldered as described in the Proper Solder-
ing Techniques section of this manual.
3. Make sure that the tubes light up properly.
4. Check the tubes with a tube tester or by substitu-
tion of tubes of the same types and known to be
good.
5. Check the values of the parts. Be sure that the
proper part has been wired into the circuit, as
shown in the Pictorial Diagrams and as called
out in the wiring instructions.
6. Check for bits of solder, wire ends or other
foreign matter which may be lodged in the wir-
ing.
7. If, after careful checks, the trouble is still not
located and a voltmeter is available, check vol-
tage readings against those shown on the
Schematic Diagram. NOTE: All voltage readings
were taken with an 11 megohm input vacuum
tube voltmeter. Voltages may vary as much as
10% .
8. A review of the Circuit Description will prove
helpful in indicating where to look for trouble.
NOTE: In an extreme case where you are unable to
resolve a difficulty, refer to the ‘Customer Service”
information inside the rear cover of the Manual. Your
Warranty is located inside the front cover.