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During transmit conditions, only tube V3 is
switched out of the circuit, with all other circuits
operating. B+ is supplied to V5, V4A and V1B
while the cathode of the final amplifier V4B
is returned to ground. With B+ removed from
the receiver section V3, no audio voltage appears
across the volume control R13 and only the
signal which is amplified by the microphone pre-
amplifier V1B reaches the grid of the audio
driver stage V1A.
External radio frequency energy is prevented
from re-entering the audio circuitry via the
microphone cable through the use of RF choke
RFC6 and capacitor C41 in the microphone in-
put circuit. In transmit, the volume control will
have negligible effect on the amount of audio
impressed on the RF carrier, the volume control
being isolated by resistor R22. It will be found
that fixed gain in the microphone audio circuit is
adequate for all normal transmit conditions.
POWER SUPPLY SECTION
The internal power supply provides the voltages
necessary for proper operation from any 105-
125 volt 50/60 cycle source. The B+ voltage is
produced in a full -wave voltage doubler circuit
consisting of D2, D3, C31 and C32. This DC
voltage is then filtered by C33A and C33D, and
distributed to the proper circuit points. Approx-
imate B+ requirements are 260 volts 45 ma
during receive and 90 ma during transmit.
The power connector on the chassis rear apron
permits operation from any external source
offering the proper voltages. The filament wiring
is so arranged that the tubes are connected for
either 6 or 12 volt operation, depending upon
which power cable is in use. For 117 V AC
operation, the power transformer provides 6.3 V
AC for parallel wired filaments.
CONSTRUCTION NOTES
This manual is supplied to assist you in every
way to complete your kit with the least possible
chance for error. The arrangement shown is
the result
and
trial. If followed carefully, the result will be a
stable instrument, operating at a high degree
of dependability. We suggest that you retain the
manual in your files for future reference, both
in the use of the instrument and for its main-
tenance.
UNPACK THE KIT CAREFULLY AND CHECK
EACH PART AGAINST THE PARTS LIST. In so
doing, you will become acquainted with the parts.
Refer to the charts and other information on the
inside covers of the manual to help you identify
the
components.
If some shortage or parts
damage is found in checking the Parts List,
please read the REPLACEMENT section and
supply the information called for therein.
Resistors generally have a tolerance rating of
10% unless otherwise stated in the Parts List.
Tolerances on capacitors are generally even
greater. Limits of +100% and -20% are common
for electrolytic capacitors.
We suggest that you do the following before work
is started:
1. Lay out all parts so that they are readily
available.
2.
Provide yourself with good quality tools.
Basic tool requirements consist of a screw-
driver with a 1/4" blade; a small screw-
driver with a 1/8" blade; long -nose pliers;
wire cutters, preferably separate diagonal
cutters; a pen knife or a tool for stripping
insulation from wires; a soldering iron (or
gun) and rosin core solder. A set of nut
drivers and a nut starter, while not neces-
sary, will aid extensively in construction of
the kit.
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