GE BC-375-E Preliminary Instructions

PRELIMINARY INSTRUCTIONS

FOR

RADIO TRANSMITTER BC-375-E

AND

ASSOCIATED EQUIPMENT

Manufactured by

GENERAL ELECTRIC COMPANY

U.S.A.

PUBLISHED BY AUTHORITY

OF

THE CHIEF SIGNAL OFFICER

Order No. 16-WFSCPD-42

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TABLE OF CONTENTS

SECTION I

DESCRIPTION OF COMPLETE EQUIPMENT

Par.

1.

General

2.

General

3.

Radio Transmitter BC-375-E (Includes Mounting FT-151-A)

4.

Dynamotor Unit PE-73-C
Cords

5.

6.

Antennas

7.

Antenna Tuning Unit BC-306-A  

8.

Reel RL-30-B and Connector Clamp MC-163

9.

Interconnection with the Radio Receiver in Aircraft

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SECTION II

INSTALLATION

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Page

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1

1
1
1
2
2
2
2
3

10.

General

11.

Radio Transmitter BC-375-E .

12.

Operation at High Altitude ....

13.

Dynamotor Unit PE-73-C

14.

Radio Transmitter Adjustment

15.

Antenna Adjustments

16.

Dynamotor Unit PE-73-C

17.

Reel RL-30-B

18.

Operating Routine... .

19.

Summary Covering Normal Operation

20.

Inspection

21.

Lubrication

22.

Service Notes

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SECTION III

PREPARATION FOR USE

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MAINTENANCE AND REPAIR

SECTION IV

OPERATION

SECTION V

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3
3
4

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4

4
6
8
8
9

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9

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10

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10

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LIST OF ILLUSTRATIONS

Fig. 1. Radio Transmitter BC-375-E, Schematic Diagram

Fig. 2. Radio Transmitter BC-375-E, Connection Diagram

Fig. 3. Radio Transmitter BC-375-E, Dimensions and Weights

Fig. 4. Transmitter Tuning Units, TU-5-B, TU-6-B, TU-7-B, TU-8-B,
TU-9-B, TU-10-B, and TU-26-B ; Schematic Diagrams

Fig. 5. Transmitter Tuning Unit TU-5-B, Connection Diagram

Fig. 6. Transmitter Tuning Unit TU-6-B, Connection Diagram

Fig. 7. Transmitter Tuning Unit TU-7-B, Connection Diagram

Fig. 8. Transmitter Tuning Unit TU-8-B, Connection Diagram

Fig. 9. Transmitter Tuning Unit TU-9-B, Connection Diagram

Fig. 10. Transmitter Tuning Unit TU-10-B, Connection Diagram

Fig. 11. Transmitter Tuning Unit TU-26-B, Connection Diagram

Fig. 12. Case CS-48, Dimensions and Weight

Fig. 13. Dynamotor Unit PE-73-C, Connection Diagram

Fig. 14. Dynamotor Unit PE-73-C, Dimensions and Weights

Fig. 15. Antenna Tuning Unit BC-306-A, Connection Diagram

Fig. 16. Antenna Tuning Unit BC-306-A, Dimensions and Weights

Fig. 17. • Mounting FT-115-B, Dimensions and Weight

iv

SECTION I

DESCRIPTION OF COMPLETE EQUIPMENT

1. GENERAL
Radio Transmitter BC-375-E with its associated

equipment is designed for aircraft and for applica­tions requiring a medium power equipment with the
characteristics of strength, light weight, flexibility
and portability. The equipment is designed to provide
communication by voice, tone, or continuous-wave
telegraph over the frequency range of 150 to 12,500
kilocycles. However, only the frequencies covered by
the transmitter tuning units listed in next column
are available for use with this equipment.

Suitable tuning equipment is provided in the radio

2.

GENERAL

Radio Transmitter BC-375-E and associated equip­ment are part of aircraft radio sets. Installation con­ditions vary widely, and no detailed single set of
installation instructions can be given in this book.

However, separate instructions are furnished for each
radio set and only such general instructions as can be
followed in all installations are given in the following

paragraphs.

The requirements for shielding and bonding of
cords in aircraft installations are very rigid, so that
difficulties with extraneous pick-up from the radio
receiver side tone and radio frequency from the
power supply will be minimized.

RADIO TRANSMITTER BC-3 7 5-E

3.
(Includes Mounting FT-1 5 1-A)

The radio transmitter outline dimensions and

weights are shown in 1'ig. 3.

The radio transmitter should be located in relation

to its associated equipment so that dynamotor and

antenna leads will be of minimum length. Two types
of shock-absorber mountings are available for use with
the radio transmitter: Mounting FT-151-A is a tray­type and is part of the Radio Transmitter BC-375-E.
Mounting FT-115-B is a disposable-type. The tray-

type mounting, to which the radio transmitter is

attached by four snap-slide catches, is normally
used. The disposal mounting is sometimes added
near the top of the radio transmitter to prevent
swaying. Mounting FT-115-B consists of a rubber
button in a steel shell which may be attached to the
top, bottom, or sides of the radio transmitter. Certain
of the radio transmitter-cover fastening screws have
been placed so as to allow attachment of this mount­ing.

transmitter to permit operation into a wide range of
antennas over most of the frequency range. Antenna
Tuning Unit BC-306-A may be used to extend the
range of antenna tuning for frequencies between 150
and 800 kilocycles.

1.

TU-5-B

2. TU-6-B

3. TU-7-B

4. TU-8-B

Dynamotor Unit PE-73-C furnishes the power
required by the radio transmitter and operates from a
24/28 volt storage battery or other direct-current
source used in aircraft.

SECTION II

INSTALLATION

The radio transmitter should not be mounted closer
than two inches from a wall, and in aircraft and
vehicular installations it is desirable that Mounting
FT-115-B be added at the top of the radio trans­mitter to prevent excessive swaying. The power
cords should not be fastened nearer than 18 inches
from the radio transmitter. This precaution prevents
vibration from being transmitted to the unit through
the cords. It is important that sufficient space be
allowed in the front of the radio transmitter to
facilitate replacement of tubes, removal of trans­mitter tuning units, and the making of tuning adjust­ments. After installation has been completed and
tested, the snap-slide catches should be securely
safety-wired at the places provided.

4.

The dynamotor unit should be mounted in an
accessible position to allow access to the relay-fuse
box, keeping in mind that the length of the leads from
the battery to the dynamotor unit must be as short as
practicable. This unit when operated in conjunction
with Radio Transmitter BC-375-E draws from 20 to
30 amperes. No. 6 Awg or larger conductor should
therefore be used for these leads in order to keep
the voltage drop at a minimum. Mounting FT-107
should be securely attached so that the dynamotor
unit cannot be torn loose by acceleration, vibration
or shock.

After the dynamotor unit is clamped securely to
Mounting FT-107 by means of the four snap-slide
catches, Plugs PL-59 n,nd PL-61 of the applicable
cords should be plugged in Sockets SO-39 and SO-41,
respectively on the dynamotor unit. The primary leads
from the battery should then be clamped securely to
the proper binding posts on the dynamotor unit ter­minal board.

1500-3000 kc
3000-4500 kc
4500-6200 kc
6200-7700 kc

5. TU-9-B

6. TU-10-B

7. TU-26-B

DYNAMOTOR UNIT PE-73-C

7700-10,000 kc

10,000-12,500 kc

200-500 kc

1

5. CORDS

The cords to be used with the various radio sets

are listed in the parts lists for same. Schematic

diagram (Fig. 1) shows the necessary cording for the

Radio Transmitter BC-375-E. Plug PL-64 and Socket

SO-44 contain the necessary interconnections for the

radio receiver and transmitter control.

6. ANTENNAS

Because of the wide variety of antennas in the
radio sets of which Radio Transmitter BC-375-E is
a part, no specific details will be given for antenna

installations. However, the following general pre-

cautions should be observed:

1.

The antenna and ground leads should be made

as short as possible, except where the length of lead-in
is definitely determined by the placement of radio
set and antenna.

2.

Antenna leads should be insulated to withstand

radio-frequency potentials as high as 5000 volts.

3.

Antenna leads should be so placed that operat­ing personnel will not come in contact with them
during normal operation of the equipment. Points

accessible to personnel should be covered with
Isolantite beads.

4.. Ground connections should have as low resist­ance as possible. In aircraft installations the ground
path should be well bonded. The GND post should
always be connected to the ground system by a
short lead, allowing, of course, for flexure due to

vibration and shock. A link will be required between
posts LOAD A and LOAD B when Antenna Tuning
Unit BC-306-A is not used.

5. Antenna leads between the antenna and radio

transmitter and between the radio transmitter and

the radio receiver should be located as far as possible
from any primary wiring of the airplane. This applies
especially to the wiring to the dynamotor unit and is
necessary in order to decrease the pick-up of electrical
interference by the antenna circuit wiring.

7. ANTENNA TUNING UNIT BC-306-A

This tuning unit is provided with Mounting FT-142.
It should be mounted so that the tuning controls will
be accessible during operation. It is desirable that the

length of leads between the.radio transmitter and the
antenna tuning unit be kept to a minimum and that
the leads be well insulated.

' Terminals A-TRANS and B-ANT on the antenna

tuning unit are connected to LOADING TERMI-

NALS A and B respectively on the radio trans-

mitter when operation is with the low-frequency
transmitter tuning unit (Transmitter Tuning Unit

TU-26-B). However, at high altitudes (above 15,000

ft) and frequencies below approximately 400 kc,

better operation may be obtained by connecting

terminal A-TRANS on the antenna tuning unit to
the antenna post on the radio transmitter; placing a
jumper between LOADING TERMINALS A and B
on the radio transmitter; and connecting the antenna
to terminal B-ANT on the antenna tuning unit. This
alternate connection should be used only if it is
necessary to reduce the r-f voltages at the radio
transmitter because of high altitude flashovers. The
sensitivity of the radio receiver may be reduced
slightly. The post marked GND on the antenna
tuning unit should always be connected to the radio
transmitter ground.

8. REEL RL-30-B AND CONNECTOR
CLAMP MC-163

The reel should be mounted in such a position that

the crank is readily accessible and the counter is
visible. In order to prevent excessive "piling" when
the wire is being reeled in, the reel should be mounted
at least six inches above the fairlead and so placed
that the point at which the antenna wire leaves the
spool is in line with the axis of the fairlead; that is,
for best operation there should be no bends in the
antenna wire between the point where it leaves the
reel and the far end of the fairlead. The four mounting
bolts can be inserted in the reel base through the hole
provided in the web of the spool. Unless the mount­ing screws themselves are grounded, a heavy ground­ing wire or strap could be clamped under the nut of
one of the mounting screws for the purpose of thor­oughly grounding all metal parts of the reel.

To fasten the antenna wire to the bottom of the

spool channel it is first necessary to remove the
spool cover by withdrawing it forward over the spool.
This can best be done by placing the fingers of both
hands on opposite sides of the cover and pressing
on the spool with the thumbs. The end of the wire
should be looped under the anchor pin in the spool hub
and then twisted around the wire proper a few times.
The twisted loop should then be placed in the groove
and all of the wire wound on the spool by turning the
crank in a clockwise direction. At this point the cover
should be replaced by passing the wire through the
slot opposite the wire opening and pushing the cover
over the spool until it rests against the flange on the
back plate. The cover should now be rotated so that
the wire from the fairlead to the spool will not rub the
edges of the wire opening in the cover either when
the spool is full or nearly empty. The counter should
now be set to zero. This should be done each time the
reel is used in order to reduce the error in the reading
caused by irregularities in winding.

Electrical connection to the radio transmitter is

made by means of Connector Clamp MC-163, the
installation of which is as follows :

a.

Remove the brass bushing from Connector

Clamp MC-163 by loosening screw in top of cover

2

and fasten the antenna lead from the radio transmitter
to this bushing by means of the screw provided.

Replace the bushing in cover and place the con-

b.
nector over the top of the fairlead, clamping it into
place by means of the screw in the side of the cover.

c.

Wind the desired amount of Wire W-106 or
W-106-A on the spool and feed the free end through
the connector clamp and fairlead until it touches the
ground below the airplane.

d.

Connect the free end of the wire to the cable

loop on the Weight WT-7-A or WT-7-B. Considerable

care should be taken in making the connection
between the antenna wire and the weight cable in
order that the joint will run smoothly through the
connector clamp when the antenna is being let out or
reeled in. The loop formed in the antenna wire should
be as small as practicable and the section where the
antenna wire is twisted back upon itself should be
tapered and made as short as a safe joint will permit.

Wind up the antenna wire in the reel until the
Weight WT-7-A or WT-7-B rests securely in the
fairlead socket. Let out and reel in approximately
ten feet of the antenna several times (have someone
pull lightly on the weight to keep the antenna wire
tight) to insure that the connector clamp is working
properly and that the joint between the antenna

wire and weight cable runs smoothly through, the
clamp.

Fairlead Extension F-9 is used when the standard
Fairlead F-8 is not long enough. It consists of Cou­pling MC-161 and a 36-inch length of standard
phenolic tubing of the same cross section as the tube
of Fairlead F-8. The extension is installed by slipping
Coupling MC-161 over the top of the fairlead tube so
that it covers approximately 3 inches of the tube
and then securing it in place by means of one of the
clamps provided. The tubing may then be clamped
into the coupling by means of the remaining clamp.
This tubing may be cut to fit a particular installation
or more than one extension may be used if required.

9. INTERCONNECTION WITH THE RADIO RE-

CEIVER IN AIRCRAFT

It is necessary, in order to minimize receiver noise,
that the cord shields be well grounded and so sup­ported that they cannot rub on other cords or metal
surfaces. In order that the radio receiver used be co­ordinated with the radio transmitter, the receiver
control wires should be connected to terminals 21
and 22 of Plug PL-64. These points are normally
closed but are opened when the key is closed and the
radio transmitter starts functioning.

PREPARATION FOR USE

10.

GENERAL

After installation and before the equipment is put

into operation, the circuits of all cords and ex t erna

wiring should be checked to insure compliance with

the circuit diagram and the applicable intercon-

nection diagram. This circuit check should be made
with all plugs removed from the sockets in the radio
transmitter and power unit to determine that all cord

and junction box connections are made as indicated

on the diagrams. A voltmeter and battery may be

used for this purpose. The plugs should be replaced
in their respective sockets after this check.

RADIO TRANSMITTER BC-375-E

11.
The following procedure is recommended for pre-

paring the radio transmitter for use after installation.

Remove Plug PL-59 from the power unit or

a.

dynamotor unit and cover its socket with a Socket
Cap M-164-A.

b.

Remove the tube compartment shielding cover
and insert the tubes. From the front of the radio
transmitter, progressing from left to right, the tubes
are as follows:

SECTION III

is not designed for alternating-current operation.)

Tube VT-25—Speech Amplifier
Tube VT-4-C—Master Oscillator
Tube VT-4-C—Power Amplifier
Tube VT-4-C—Modulator
Tube VT-4-C—Modulator

c.

D-c Filament Supply:

(1).

Remove all links from the filament resistor

connection board.

(2).

Assuming that the primary source voltage
is 28 V (the terminal voltage of a 24-volt storage
battery under charge), place the 24 V/28 V switch
in the tube compartment in the 28-volt position.

(3).

Set the transmitter signal switch on CW

and the filament voltmeter switch on CW FIL.

(4).

Place the OFF-ON switch in the ON
position. This should start the dynamotor unit and
apply filament supply potential to the radio trans­mitter, but not to the tubes. Connect link between
adjacent studs on the 28 V and CW FILAMENT
rows. The CW filaments will light and the fila­ment voltmeter read. Repeat this until the two
studs are found that when connected will cause

(Note: This equipment

3

the filament voltmeter to read 10 volts. Then place
the OFF-ON switch in the OFF position and
connect a link between the two studs just selected.

Set the radio transmitter signal switch on

(5).
VOICE and the filament voltmeter switch on
MOD. FIL. Repeat the operation of (4) for the
28 V and MOD. FILAMENT rows of studs.

Again place the OFF-ON switch in the ON

(6).
position. Set the filament voltmeter switch on
CW FIL. (signal switch on VOICE). The CW
filament voltage will now be less than 10 volts.
In the same manner, connect between the adjacent

studs of the COMP and CW FILAMENT rows

until the filament voltmeter again reads slightly

over 10 volts. The OFF-ON switch may then be

placed in the OFF position and this link fastened
in the proper place.

Cut off the charging generator, place the

(7).

24 V/28 V switch in the 24-volt position and in a
similar manner to the preceding select the proper
studs on the 24 V and CW FILAMENT rows and
the 24 V and MOD. FILAMENT rows so that the
filament voltmeter will indicate 10 volts in either
position. As now adjusted the filament voltages
will not require further adjustment unless the
cable lengths or charging rates are changed. Ordi­narily, in aircraft installations, a battery-charging
generator is used at all times. The 24 V/28 V switch
should accordingly be placed in the 28-volt position.
If it is desired to check the operation of the radio
equipment when the charging generator is below
operating speed, this switch should be changed to
the 24-volt position since operation at low voltage

will reduce the life of the tubes.

Replace Plug PL-59 in the dynamotor unit or

d.

power unit.

NOTE : It will be noted that the filament volt-

meter will show from 0.3 volt to 0.5 volt rise when the

transmitter key is closed and plate current is being
drawn.

This is a normal condition of the radio transmitter
circuits and should be ignored, providing the above
filament adjustment has been made correctly.

OPERATION AT HIGH ALTITUDE

12.

Radio Transmitter BC-375-E and associated equip­ment may be expected to give satisfactory service on
CW at all altitudes up to 27,000 feet. On TONE and
VOICE, however, insulation breakdown may be
experienced with Transmitter Tuning Unit TU-8-B

(6200-7700 KC) above 25,000 feet and with Tuning
Unit TU-9-B (7700-10,000 KC) above 19,000 feet.
These altitude limitations may be exceeded slightly
by care in tuning and by carefully guarding against
accumulation of dust and other foreign matter in the

equipment. Complete assurance of effective operation

between 6200 and 10,000 kilocycles at altitudes
between 19,000 and 27,000 feet may be had on CW
alone. Transmitter Tuning Unit TU-26-B may be
expected to give satisfactory service at all altitudes
up to 15,000 feet.

13.

DYNAMOTOR UNIT PE-73-C

Before being used for the first time, it is recom­mended that the end bells of the dynamotor unit be
removed to make certain that the armature rotates
freely in its bearings, and a check should be made to

determine how much time has elapsed since the
dynamotor unit was last serviced. If this time exceeds
five months, follow lubrication instructions appearing
in this book. Do not lubricate more often or add more
lubricant than is specified in those instructions.

The voltage at the input terminals of the dyna-

motor unit must be 28 volts in order to obtain rated
power output from the radio transmitting equipment.

14. RADIO TRANSMITTER ADJUSTMENT
WARNING: Operation of this equipment in-

volves the use of high voltages which are dangerous
to life. Operating personnel must at all times observe
all safety regulations. Do not change tubes or make

adjustments inside equipment with high voltage
supply on. Do not complete or maintain any con­nection between radio transmitter and dynamotor
unit unless all shields on the transmitter are in
place.

SECTION IV

OPERATION

Assuming that the installation and preliminary
adjustments have been made in accordance with
SECTIONS II and III. the following operating pro­cedure is recommended. Some of these adjustments
need be made only at the time of installation.

Under no conditions should any of the switches on
the radio transmitter or tuning unit be changed with
the key or microphone button depressed. Insure that
all switches position correctly; do not attempt to leave
switches between points. Failure to observe this pro­cedure causes undue arcing of the switch and severe
strain on the vacuum tubes.

4

a. CW Operation:

unit for the desired frequency. CW operation may
then be obtained as follows:

(1).

Place the signal switch on CW.

(2).

From the calibration chart on the front of
the transmitter tuning unit, set the band change
switch A, the M.O. TUNING Control, and the

P.A. TUNING Control for the desired frequency,

and set the ANT. COUPLING SWITCH D on

Point 1. (It should be remembered that the band
change switch does not appear on Transmitter
Tuning Units TU-7-B to TU-10-B inclusive.)

(3).

Place the OFF-ON switch on the ON
position. The dynamotor should now start and the
m-o and p-a filaments will light. In case repeated
failures of Fuse FU-22 are encountered and if such
failures persist after compliance with instructions
pertaining to Dynamotor Unit PE-73-C, it is
recommended that Fuse FU-22 be removed from
the relay-fuse box and one extra Fuse Link M-168
inserted in the fuse cartridge. Fuse FU-22 will then
have two fuse links in it and should be replaced
in the relay-fuse box of the dynamotor unit. In no
case should the use of more than two fuse links be
attempted.

(4).

Press the test key or the transmitting key.
The vacuum tubes will now draw plate current as
indicated by the TOTAL PLATE CURRENT
METER. The p-a tuning should be checked
immediately for resonance by varying the control

slightly until a minimum total plate current is
indicated. When the p-a circuit
nated, the total plate current will be from 80 to
110 milliamperes.

(5).

The antenna should next be tuned to

resonance. Because a wide variety of antennas is
possible, no specific instructions for antenna
tuning are given other than instructions to effect
antenna resonance by means of the controls pro­vided on the transmitter, and on the antenna tuning
unit whenever the latter is in use. The subject of
ANTENNA ADJUSTMENTS (paragraph 15) is
considered more in detail elsewhere in this instruc­tion book, and should be referred to in preparation
for operation of the equipment.

Antenna resonance is indicated by a reading of
current on the ANT. CURRENT meter and by an
increase in total plate current. The increase in
plate current is the more sensitive indication of

approaching antenna resonance. When the antenna
is tuned to resonance, the total plate current
reading will be somewhat higher than the off
resonance value. If the plate current is below 200
to 220 milliamperes, the coupling to the antenna
should be increased by placing control D on a
higher point and the antenna circuit retuned.

When finally adjusted, the total plate current

Select the transmitter tuning



properly reso-

should read from 200 to 220 milliamperes. If
necessary, detune the antenna circuit slightly,
keeping the p-a dial C in resonance to keep within
the plate current limits.

(6).

The equipment is now delivering rated
power output, and the transmission may be carried
on by operating the transmitting key. In order to
shut down the equipment, it is necessary only to
place the OFF-ON switch in the OFF position.

b.

Voice Operation:

ment has been placed in operation on CW, the
following procedure is recommended for obtaining
voice operation. Note the value of total plate current
for CW operation. Then place the signal switch in
the VOICE position and, by means of the MOD.
BIAS adjustment in the tube compartment, adjust
until the total plate current with the microphone
switch depressed is approximately 20 to 35 milli­amperes higher than for CW. The modulator tubes
are now biased nearly to cutoff for proper Class B
operation, and radiophone communication may be

.

carried on by speaking into the microphone. It will be

noted that the total plate current increases when the
microphone is spoken into. This increase is due to
current drawn by the modulator tubes. With sustained
normal level of speech impressed on the microphone,
the plate current should rise to an average of 300
milliamperes. If this value is not obtained, the

INPUT LEVEL control in the tube compartment
can be adjusted until the proper amount of modula­tion, as indicated by the correct plate current, is
obtained.

c.

Speech-amplifier Bias:

amplifier bias will usually be found betWeen 6.0 and

7.5 on the bias adjustment dial. Settings in this range
will normally give the proper speech-amplifier plate
current and optimum side-tone frequency on all
tuning units.

d.

Tone Operation:

been adjusted for VOICE operation, it is necessary
only to place the signal switch on TONE for proper
tone telegraph operation. The total plate current on
TONE will usually be between 300 and 350 milli­amperes.

e.

Side Tone in Aircraft Set:

circuits have been properly co-ordinated with the
radio transmitter, the receiver control' circuit will
operate each time the transmitting key or microphone

switch is closed, and the transmitter side tone will be
supplied to the headset. When the key or the switch
is opened the receiver again becomes operative, thus
allowing break-in operation. The SIDE TONE level
control located in the tube compartment, is used
to adjust side tone to a suitable value for any par­ticular installation. It will be noted that a higher level
is desirable on voice position than on the CW and
TONE positions.

Assuming that the equip-

The correct speech-

After the equipment has

If the radio receiver

5

The side-tone control is a four-position switch, two
positions of which are used for high-level and low-level
side-tone signals for a 2000-ohm load, and the other
two positions are used for the high-level and low-level
side-tone signals for a 150-ohm load. With the side­tone control set in the 2000-ohm high-level position
(4), the output voltage will be between 17% and 30
volts. In the 2000-ohm low-level position (3), the
output is approximately 10 volts. The output in the
150-ohm high-level position (2) will be between 4.5
and 7.5 volts. While the 150-ohm low-level position
(1) will give approximately 2.5 volts, the operator

should determine the headset resistance and select
the correct side-tone switch position at the time of
installation.

f . Calibration Reset:

facturing tolerances, the inter-electrode capacity of a

vacuum tube varies between limits fixed for each
particular type of tube. Since the tube capacity is an
appreciable part of any master-oscillator circuit, it is

impossible to make up a calibration chart which

will be exactly accurate for all tubes whose capacities
are within the allowable limits. For this reason
Radio Transmitter BC-375-E is provided with a
calibration reset capacitor which enables the operator
to reset the radio transmitter frequency to correspond

with the calibration chart when the set is first placed

in operation and thereafter whenever the master­oscillator tube is changed. A heterodyne frequency
meter or other standard of frequency is required.
The procedure is as follows:

(1).

Allow radio transmitter to warm. The
operator will obtain the most accurate results by
allowing the radio transmitter to "warm up" on

key locked CW for a period of at least 20 to 30

minutes before set Ging the calibration reset capac­itor or checking the calibrated transmitter
frequency.

(2).

With the transmitter tuning unit for the
highest working frequency placed in the radio
transmitter, tune the transmitter for CW operation
on one of the calibrated frequencies at the high
frequency end of the band. (Approach the cali­brated point by proceeding from a lower dial
reading to a higher one.)

(3).

Place the frequency meter in operation and
adjust it to the frequency indicated on the trans­mitter calibration in accordance with the operating
instructions and calibration chart furnished with
the frequency meter. The calibration accuracy of
this frequency meter should be 0.01 per cent, or
better.

(4).

Open the calibration reset port, located on
the front panel, between the TEST KEY and
TONE-CW-VOICE switch, insert a screwdriver,
and rotate the calibration reset capacitor until the

Due to necessary manu-

transmitter frequency coincides with that of the fre­quency meter or standard.

Close the calibration reset 'port.

(5).

The transmitter calibration is now reset for any
tuning unit of the same order number and serial
number as the radio transmitter and the accuracy
of calibration will be within 0.05 per cent plus the
accuracy of the standard. The calibration must be
checked in this manner each time the m-o tube is
changed.

15. ANTENNA ADJUSTMENTS

The antenna is, in general, a system of conductors
which, when excited by a radio-frequency voltage,
sets up an electromagnetic and electrostatic field
causing a component of this field to travel away
from the antenna with the velocity of light.

The radiation characteristics of antennas, direc­tivity, and radiation efficiencies are determined by
their physical shape and location with respect to other
bodies. In aircraft, since there is no wide latitude in
physical design of fixed antennas, the problem be­comes mainly one of determining the best methods of
operating available designs.

It is necessary first to determine how the antenna
impedances vary at the operating frequencies in order
that the loading facilities may be properly used.
The reactance of an antenna may be approximated
from the theory of transmission lines in which uni­formly distributed inductance and capacity are
assumed, resistance and insulator leakage being
neglected.

Selecting a certain length of antenna and plotting
its reactance variation with frequency, we obtain
repeating cotangent curves. It may be seen that at
certain frequencies the reactance becomes zero.

Under these conditions, the antenna is "resonant,"

analogous to a simple-series circuit turned to reso-

nance.

It may be noted that the "series" resonant points
occur at all odd multiples of the first resonant fre­quency, which is called the fundamental frequency.
The fundamental frequency, the third harmonic,
and the fifth harmonic, all points of zero reactance,
correspond to a voltage distribution along a simple
vertical wire of "quarter-wave," "three-quarters
wave," and "five-quarters wave." Antennas of this
type, operated at zero or low reactances, are com­monly called "current fed"; that is, they require low
driving voltages for their operation.

At even multiples of the fundamental frequency, it
may be seen that the antenna reactance is very high.
Operation at the second and fourth harmonics corre­sponds to "half-wave" and "full-wave" operation.
Under these condicions, antennas are "voltage fed" ;
that is, they require high driving voltages.

6

The resistance component of the antenna imped­ance is made of two parts: radiation resistance which
represents the radiation of power or waves away
from the antenna and which is productive of a useful
result; and loss resistance which is a combination of
losses due to conductor and ground resistance, and to
dielectric hysteresis. Loss resistance performs no
useful function and every effort should be made to
maintain it very small in comparison with the radia­tion resistance. The efficiency of an antenna with
respect to radiation of power may be expressed as the
ratio of radiation resistance to total antenna resist-

ance.

Antenna resistance varies over wide limits with

frequency. The resistance values approach very high

values at the even harmonics, and minimum values
at odd harmonics. It is thus seen that the operation
of a radio transmitter over a wide frequency band
requires that the radio transmitter be capable of
providing a considerable range of output voltages.
This is accomplished in each transmitter tuning unit

by a six-point ANT. COUPLING SWITCH, D. In
order that the voltage range required be kept a mini­mum, antennas are usually "resonated" ; that is, they

are series tuned by either inductance or capacity as

may be necessary so that the required output volt­age range depends only on the antenna resistance

variation over the desired frequency range.

When operating antennas at frequencies lower than

their fundamental or odd harmonics, they appear
to the antenna tuning equipment as a capacity in
series with a resistance. In order to balance out this
capacitive reactance, it is necessary to load the

antenna by means of an inductance, the reactance of
which is made equal to that of the apparent antenna
capacity. For operation of antennas at frequencies

higher than their fundamental and odd harmonics,

the converse is true, a capacity in series with the
antenna being necessary in order to balance the
apparent antenna inductive reactance.

In most cases, except where 3/4- and 5/4-wave

trailing wires are used for high frequencies, antenna

operation will be around the fundamental frequency.

In general, it may be said that if antennas are
operated so that their effective length is an appreciable
percentage of the operating wavelength, they will
have marked directive properties. This corresponds to
operation near to and higher than the fundamental
frequency. When antennas are operated at frequencies
much lower than the fundamental, the ratio of
radiation to total resistance is less favorable, but the
directive properties are not nearly so evident. The
fundamental frequency of an antenna depends mainly
on its effective length including the ground lead.

Fundamental frequencies in the range of 2500-7000
kilocycles will be the most common with the usual
types of fixed antennas, while fundamentals as low as

1500 kilocycles will be obtained with 200-foot trailing­wire antennas.

The antenna tuning equipment in the radio trans­mitter is designed to feed antennas at any frequency
from 800 to 12,500 kilocycles. Over this band of fre­quencies it is necessary to feed antennas at, above and
below their fundamental frequencies. Therefore, the
circuit and circuit constants are so selected as to per­mit of both current and voltage feed. A rotating
inductor and a tapped inductance provide the induc­tive reactance variation. A variable capacitor pro-

vides the variation in capacitive reactance and also

serves as a coupling impedance for voltage feed.

Controls governing the variation in inductive or
capacitive reactance are so arranged that inductance
or capacitance is increased with increase in dial
reading.

With the ANT. CIRCUIT SWITCH, N, bn
position 1, the radio transmitter works into a simple
series resonant circuit, in which the high voltage
built up across the antenna tuning capacitor is used to
"voltage feed" the antenna. This circuit is generally
used for high frequencies and fairly long fixed antennas.

The antenna feed circuit is maintained at resonance
by means of ANT. IND. TUNING, M, while the
voltage fed to the antenna is varied by means of
ANT. CAP. TUNING, 0, and ANT. COUPLING
SWITCH, D. Feed circuit resonance is indicated
by the ANT. CURRENT meter. The current in the
feed circuit is adjusted by control D and should not
exceed 6 amperes. The step-by-step tuning procedure
is as follows:

(1).

Set control 0 at some arbitrary scale read-

ing.

(2).

Resonate circuit by means of control M for a

maximum reading on ANT. CURRENT meter.

(3).

Adjust control D so that antenna ammeter

reads below 6 amperes.

(4).

Re-resonate circuit as in 2.

Repeat the above procedure until the proper loading

(200-220 ma on CW) is indicated on the plate am­meter. The lower the dial reading on control M and

the lower the reading on the ANT. CURRENT
meter that it is possible to obtain at a given frequency,
the more power will actually be delivered to a given
antenna. The lower the reading on control M and the
lower the ANT. CURRENT readings, the less the
tuning circuit losses and thus the more useful power is
delivered to the antenna for radiation purposes.

With ANT. CIRCUIT SWITCH, N, on position 2,
the radio transmitter works into a series resonant cir­cuit where the antenna is "current fed." The antenna
circuit is resonated by means of ANT. IND. TUN-

ING, M, and ANT. CAP. TUNING, 0, as indicated
by the ANT. CURRENT meter. This circuit is used
generally for operation near the fundamental fre-

quency of the antenna.

7

With control N on position 3, the radio transmitter
works into a series resonant circuit providing "current
feed" and inductive loading. The antenna circuit is
resonated by means of a continuously variable
rotating inductor, control M. This circuit is used for
operation below the fundamental frequency of the
antenna.

With control N on position 4, the antenna circuit
is identical with that obtained on position 3 except
that an additional tapped inductance, controlled by
ANT. IND. SWITCH, P, is added in series with the
rotating inductor. This circuit is used when the
operating frequency is relatively far below the funda­mental frequency of the antenna.

It is recommended that the operator check the
possible resonance of coil, item 1170 of Fig. 1, at
operating frequencies above 4500 kilocycles. Although

this coil is not connected in the antenna circuit, the

inherent capacity coupling may cause absorption of
useful radio-frequency power. Absorption may be

easily determined by placing control switch P at sev­eral points while watching the antenna current. Con-

trol P must not be allowed to remain at a point which

indicates a decrease in antenna current. In general,
it will be found that no difficulty will occur if the
following points are used.

Transmitting Tuning Unit

TU-7-B
TU-8-B
TU-9-B
TU-10-B

The antenna resonance is then made in the usual

manner using controls M, N, and possibly 0.

For operation in the frequency range of 150 to 800
kilocycles, the externally connected Antenna Tuning
Unit BC-306-A is used. This unit contains the neces-

sary inductive reactance to resonate specified antennas

at frequencies well below their fundamental. The

variation in inductive reactance is provided by the
ANTENNA VARIOMETER SWITCH, control E,
and the ANTENNA VARIOMETER, control F.
The proper connections are described in SECTION

INSTALLATION. In general, it will be necessary
to use Antenna Tuning Unit BC-306-A with Trans-

mitter Tuning Unit TU-26-B. The antenna loading
equipment contained in the radio transmitter will
resonate a 400 micromicrofarad antenna to approx­imately 650 kilocycles. Therefore when the minimum
inductance is reached on the Antenna Tuning Unit
BC-306-A (E = 2, F = 0), place control E in position 1
which disconnects this unit. Proceed to resonate the
antenna circuit with control N on 4. Control M is
the continuously variable inductance between induc­tance steps on control P.

P Switch Position

2
5
5
5

Under some conditions it may be found that one

coupling tap will not give sufficient loading while

the next higher tap will give overloading of the trans­mitter. In this case use the higher coupling tap by
slightly detuning the antenna circuit and keeping
the p-a dial C tuned to a minimum plate current
until the normal transmitter loading of 210 to 220
milliamperes total plate current is obtained.

•

16. DYNAMOTOR UNIT PE-73-C

Starting and stopping of the dynamotor unit is
controlled remotely by the OFF-ON switch at the
Radio Transmitter BC-375-E. No adjustments are
required or provided on the dynamotor unit.

When operated at full-rated load continuously for

M hour the temperature rise of the dynamotor will not
exceed 55 degrees Centigrade. However, if the dyna­motor is operated for a greater length of time, even at
lighter loads, without being allowed to cool off, its
temperature will continue to increase and will ulti­mately reach values which are injurious to the
insulation and may even burn out the windings.
This also applies to the starting relay. If it is desired
to operate the dynamotor unit continuously at full
load for a period greater than IA hour (such as for
testing purposes in the laboratory), the end bells of
the dynamotor and the cover of the relay-fuse box
should first be removed. The dynamotor unit can then

be operated at rated load continuously for any period

of time without injurious heating. Care should be
exercised to place guards around the dynamotor unit
when operated in this manner so that the operators
cannot come in contact with exposed high voltages.

When operated in conjunction with the transmitter,
the dynamotor operates at practically zero load unless
the key or microphone switch is closed. Continuous
operation under this condition will not result in

overheating although the transmitter should be turned
off whenever possible between the periods of trans­mission.

17. REEL RL-30-B

Braking, locking and winding operations are
controlled from the crank on the reel. Normally the
reel is in the locked position such that the wire will not

II,

unwind from the spool. Reeling-in is accomplished by
rotating the crank in a clockwise direction, as indi­cated by the direction arrow Wind on the nameplate
at the center of the reel spool. A ratchet mechanism
on the spool prevents the wire from unreeling when
the crank is released. By rotating the crank in a
counterclockwise direction the braking mechanism
is released, thereby permitting the wire to be reeled
out. Braking force decreases gradually as the handle
is rotated through approximately the first 40 degrees
of its motion. Beyond this point, and up to the

extreme limit of its motion the brake is completely

8

released and the spool is free to spin. The speed of
unwinding can be readily controlled by regulating

the braking effect with the crank. A spring return on
the crank automatically resets the brake to the normal
or locked position when it is released.

Tuning the antenna by adjusting its length should

be accomplished by allowing slightly more wire than
is necessary to run from the reel and then reeling
in slowly to obtain the proper length by observing
the resonant condition. During the reeling-out
operation, care should be taken that all of the wire
is not unreeled. The speed with which the reeling

takes place would be sufficient to snap the wire if it
reached its ultimate length, causing a loss of both the
weight and wire.

When unreeling wire, never allow the crank to
snap into the locking position when the spool is
rotating rapidly. The sudden stop which would
result may break the antenna wire and place undue
stress on the reel mechanism.

The following table gives the approximate antenna

length for various frequencies as well as the approxi­mate counter reading when 250 feet of Wire W-106
or W-106-A is wound on the spool.

1/4 Wave

ICC

2000

3000

4000
5000
6000

7000
8000
9000

10000

18. OPERATING ROUTINE

The operating routine and type of transmission to

be used will be governed by tactical requirements. The
following recommendations are given, however, to
assist in routine operation of the equipments :

a.

checked before the start of any mission.

b.

with good fuses, and that spare tubes (if carried) are in

good condition.

c.
is considerably greater than on VOICE. If distance,
atmospheric noise, etc., make VOICE communication

difficult, changing to TONE or CW will probably

improve communication.

d.
with no spares on hand, CW communication can be
carried on by inserting the good tubes in the m-o and

Length

(Ft)

123

82
62
49
41
35

31

27
24

Complete equipment operation should be

Make certain that spare fuseholders are filled

The transmission range of the equipment on CW

In case of failure of one or two Tubes VT-4-C

Counter

Reading

108

72
54
44
36
30
28
24
22

3/4 Wave

Length

(Ft)

147
123
105

93
81
73

Counter
Reading

130
108

92
82

,72

64

p-a sockets. CW operation can also be maintained
when the Tube VT-25 is removed, although no side
tone will be supplied in this event. Note that the radio­frequency and audio-frequency tubes are connected in

series parallel. If one tube is removed, another filament

will go out.

19. SUMMARY COVERING NORMAL
OPERATION

Although the normal operation of this equipment is

extremely simple after the correct installation has

been made, it is well to study the proper sequence of
various equipment procedures as summarized in the
following paragraphs. It is assumed that the installa­tion has been tested and all circuits are normal.

Do not change any switches with the key or

,microphone button depressed.

a.

To Start the Equipment:

switch at ON. The dynamotor unit will start and the

filaments will light. Unless the TONE and VOICE

emissions have been adjusted, start up initially on

CW and adjust for the desired type of emission as

given below. To control carrier depress the key.

b.

To Stop the Equipment:

place the OFF-ON switch at OFF.

c.

To Change Frequencies:

transmitter tuning unit and place in the radio trans-

mitter. Place the M.O. TUNING control, BAND

CHANGE SWITCH (if any) and the P.A. TUNING
control on the desired calibrated frequency as given

on the calibration chart. Place the emission switch
on CW, start up the radio transmitter and immediately
check the P.A. TUNING dial for minimum plate cur­rent as indicated on the TOTAL PLATE CURRENT
meter. Resonate the antenna circuit and load

to a total plate current of 210 to 220 milliamperes

with the p-a dial resonated, i.e., always tuned to a
minimum plate current. Proceed to key the carrier
on CW or select the other types of emission as given

below.

d.

To Select Any Available Type of Emission:

Start up the radio transmitter and tune for CW
transmission first as given in paragraph 19c., then,
open the key and place the TONE-CW-VOICE
switch on VOICE. Remove the tube shield and adjust
the MOD. BIAS control after key is depressed,
until the total plate current reads 20 to 35 milli­amperes above the CW value. Proceed to control
carrier by microphone button and modulate by voice,
adjust the side-tone signal to the desired level by
means of the SIDE-TONE control located in the
tube compartment. Adjust the voice level by the
INPUT LEVEL control so the total plate current

reaches 300 to
voice.

For tone transmission the operator must always

adjust transmitter for VOICE, first. Then open the

no

milliamperes on peaks of sustained

Place the OFF-ON

Open the key; then

Select the required

9

key, place the selector switch on TONE and proceed

to key carrier as in CW.

e. To Increase Power Output:

number on the ANT. COUPLING SWITCH D at
the same time keeping the P.A. TUNING dial C
and the antenna circuit in resonance. Power may be
increased until a CW plate current of 220 ma at 28
volts input is reached.

To Decrease Power Output.:

on ANT. COUPLING SWITCH D, at the same time
keeping the P.A. TUNING dial C and the antenna
circuit in resonance.

It should be noted that the CW power output may
be increased or decreased in the above manner from
the value of plate current with the antenna circuit
open to the full load rating of 220 milliamperes.
However, the TONE and VOICE carrier powers

SHOULD NOT BE INCREASED OR DE-

Go to a higher

Go to a lower number

MAINTENANCE AND REPAIR

CREASED. Unless the TONE and VOICE carriers
are adjusted as given in paragraph 19d., distortion
will result. Also, the misadjustment may cause arc­overs which would damage the equipment.

f. To Reset to the Calibration Chart,

of the m-o tube, etc.: Start the radio transmitter on
the highest frequency tuning unit available. Warm up
the radio transmitter on CW key locked for 10 to 20
minutes. The tube shield must be in place. Listen to
the calibrated frequency on a suitable accurate hetero­odyne frequency meter and adjust the radio trans­mitter to zero beat by means of a screw driver inserted
into the reset port on the.left front radio transmitter
panel. This should bring the radio transmitter back to
calibration and all other frequencies should be within

0.05 per cent. For greater accuracies reset as above to
the exact frequency desired.

SECTION V

after changing

20. INSPECTION

A thorough periodical inspection of the complete

installation at least once every 50 hours of operation

will materially aid in the maintenance of uninter-

rupted performance. The following inspection is
recommended:

a.

Determine that the storage battery is at the
proper gravity and that the charging generator and
regulator are adjusted so as to keep the battery
fully charged.

b.

Clean accumulated dust and dirt from all
units. Use an air hose or bellows, paying particular
attention to the loading coil, item 1170, in the antenna
compartment of the radio transmitter. At this time
inspect the rotating coil in this compartment. The
winding should be thoroughly cleaned using a clean
cloth moistened with naphtha or petroleum spirits.

c.

Make certain that all safety wiring is in place,
that all mounting brackets and supports are rigidly
fastened and that all nuts and machine screws are

supplied with lockwashers and are tight.

d.

Determine that no cords have broken shielding

and that all grounding and bonding is in place.

e.

Inspect plugs for proper fit and plug sockets

for compressed pin springs. Compressed pin springs,

which have taken a permanent set, can be restored by
a light hammer blow on the end of the pin.

f.

Make certain that all fuses are held tightly
in their clips. A loosely held fuse should be removed
and the clips bent with the fingers until they grip the
fuse tightly. The clips and fuse ends should be kept
clean and the contact surfaces bright.

g.

Antennas should be inspected for broken or

frayed leads, and insulators should be wiped clean.

Be sure that antenna leads have not been bent close
to metal frameworks where high antenna voltages
might cause sparkovers.

h.

Inspect keys and microphones for broken cords

and deformed plugs.

Inspect dynamotor brushes for length and

i.
broken pigtail leads. Detailed instructions on care of
brushes are given herein.

j.

Inspect both dynamotor commutators for
cleanliness and excessive wear. Information on care
of commutators is given in these instructions.

k.

Rotate the dynamotor armature by hand
to make certain it turns freely and is not rubbing
against the field poles or leads. When all four brushes
are removed, the armature should spin freely on its
bearings. Refer to detailed information on dynamotor
bearings.

21. LUBRICATION

a. Materials:

involves the use of three lubricants and several
cleaning solvents. These are:

(1).

Light Oil: A high grade, low pour test, mineral

oil with viscosity rating SAE 10.

Light Oil: A high grade, low pour test, mineral

(2).

oil with viscosity rating SAE 20.

Grease: Use only high-temperature ball-bear-

(3).
ing grease such as Grade 295, Air Corps Specification
No. 3560. "Lubrico M-21" as supplied by the Master
Lubricants Co., Philadelphia, Pa., or N. Y. & N.
Lubricant "No. 1572 Special" are recommended for
use where the temperature does not drop lower than

—31°F. Do not use unauthorized greases as they may

The lubrication of the equipment

J.

10

melt out at high temperatures or oxidize rapidly and
become gummy when packed in the bearings.

(4). Cleaning Solvents: Naphtha or petroleum
spirits are strongly recommended. Carbon tetrachloride
is used for dynamotor unit bearings and commutators.

b. Periodic Lubrication Routine

Dynamotor Unit PE-73-C:

ing conditions, the dynamotor bearings should be
lubricated in accordance with the following schedule :

After every 1000 hours of operation or at

(1).
intervals of six months, add 3 drops of SAE 20 oil
into the small oil hole which is provided in the top of
each bearing housing and is closed by a screw plug.

After every 5000 hours of operation or at in-

(2).
tervals of one year, add approximately 0.05 cu. in.

(/-in. cube) of ball bearing grease to each bearing
through the oil hole mentioned above.

NOTE: Do not add more oil or grease then speci­fied above, since the excess lubricant will tend to
work out of the bearing housing onto the commu­tators and brushes where it will cause trouble if not
wiped off. Too much grease in the bearing will have a
tendency to churn and may cause the bearing to
overheat. Always make certain that the lubricants

used are clean and that no dirt, moisture or foreign

matter enters the oil hole when adding the lubricant.

Tighten screw plugs securely into the oil holes as
soon as lubricant is added.

(3) After every 10,000 hours of operation or at
least every two years, remove the armature from
the dynamotor, thoroughly clean the bearings and

bearing housings with carbon tetrachloride and

repack each ball bearing level full of approved ball

bearing grease. See procedure for disassembly and

cleaning of bearings (paragraph 22d. (4).)

c. Reel RL-30-B:

such that it will require very little attention. The
following lubrication routine is recommended to

obtain the best operating results:

(1).

After every 20 hours of flying service apply

six drops of SAE 10 oil at the oil hole indicated on the

hub nameplate.

(2).

After every 1000 hours of flying time or every

six months, whichever comes first, do as follows:

(a)

Remove the three fillister head screws which
hold the crank handle lever to the hub and remove
the crank.

Remove the small cotter pin and castle nut

(b)

on the end of the reel shaft.

Remove reel spool and hub from the shaft.

(c)

Clean the accumulated dirt from reel

(d)

shaft and the parts in the mounting base. Examine

the exterior parts of the reel hub and clean off all dirt.

Lubricate these points using SAE 10 oil:

(e)

Counter gear shaft bearing-1 drop.
Main shaft-several drops along the bearing

surfaces.

The construction of this unit is

Under normal operat-

Rear ball bearing on hub adjacent to ratchet

teeth-5 drops.

Front thrust bearing around the edge of the

retaining nut at the front end of the hub-5 drops.

Front ball bearing around the gap between the
outside of the hub and the edge of the piece into
which the three screws from the crank handle
lever are threaded-5 drops.

(f)

Reassemble the reel as follows: Place the

reel spool and hub on the shaft. Give the spool a

slight spin clockwise until the ratchet engages the

pawls.

Replace the castle nut with the fingers, run it
down until snug and then back it off until the
hub runs free (at least IA of a turn). Replace the
cotter pin. Assemble the crank handle and tighten
the three fillister head screws.

This completes the operation of servicing the
reel.

d. Miscellaneous Lubrication

The following miscellaneous lubrication instruc-

tions should be followed in connection with the
maintenance of Radio Transmitter BC-375-E. Places
to oil and grease are listed. Do this after every 500
hours of service or at least after every 1000 hours.
Do it oftener if dirt accumulation is excessive. Clean
parts as required.

Oil SAE 20—Switch shafts in radio transmitter,

transmitter tuning units, and antenna tuning unit:
Vernier mechanisms in radio transmitter, transmitter
tuning unit, and antenna tuning unit. Variable capac­itor shafts in radio transmitter and transmitter tuning
units.

Grease—Contacts of switches, and switch position-

ing devices in radio transmitter, transmitter tuning
unit and antenna tuning unit.

NEVER lubricate the contact roller or the contact

roller shaft of the rotating antenna inductor. These
parts should run DRY and should always be kept
spotlessly clean. Naphtha or petroleum spirits should
be used to clean these parts.

22. SERVICE NOTES
In the servicing and locating of faults in the radio

transmitter and associated equipment, it is necessary
to remove various shields and covers to make the
circuits accessible. Great care must be taken in
testing with shields removed, because a great many
points of high voltage are thus exposed. Whenever
such testing is necessary, the proper procedure is to
remove all power from the equipment, make the
necessary circuit changes or meter connections and
then apply power, keeping clear of all meters which
are connected in the "high" sides of circuits where
there may exist an appreciable voltage to ground.

Always remember _that when the dynamotor is

running and the transmitting key is open, high

11

voltage is present in the radio transmitter even
though there is no plate ammeter reading.

In checking low voltage and filament circuits, the

single conductor cord with the Plug PL-59 should be

disconnected from the transmitter, thus removing
the high-voltage supply. It will be noted from
observation of the schematic diagram (Fig. 1) that
two tube filaments are connected in series. Thus, if one
fails, two filaments will go out. The defective tube can

be determined by use of a continuity meter.

The following information is supplied to aid in

servicing the equipment :

Voltage Readings

a.

(A high-resistance voltmeter should be used—at

least 1000 ohms per volt.)

(1).

Low-voltage input of 24 to 28volts, depending
on the power-supply voltage, should be obtained from
terminal 45 of Socket SO-41 to ground.

(2).

Speech-amplifier plate voltage of approxi­mately 425 volts should be obtained at the plate
connection of the speech-amplifier tube when the
transmitter is on VOICE. It is recommended that a
tube socket adapter be used which will allow not only
readings of voltages but also all currents for the Tube
VT-25.

(3).

Modulator bias voltage of 72 to 75 should be
obtained across capacitor 1160, the positive side

being at ground potential. Selector switch should be

on VOICE.

(4).

Speech-amplifier bias voltage of 35 to 40
should be obtained across capacitor 1144, the positive
side being at ground potential. Radio transmitter
switch should be on VOICE.

(5).

Plate voltage of 1000 to 1100 volts should be

obtained between terminal 61 of Socket SO-39 and
ground.

Keying voltage of approximately 200 volts

(6).
will be obtained across resistor 1115 when keying
relay 1189 is open.

(7).

Microphone-supply voltage of 4.5 to 5.3 volts

d-c should be obtained across resistor 1145.

For this test, the microphone should be in the
circuit.

b. Current Readings

Speech-amplifier plate current should be from

(1).
19 to 21 milliamperes. Adjustment of its bias voltage
to obtain this value is accomplished by potentiom­eter 1114 which is accessible in the tube compart­ment. The normal setting of this potentiometer will
usually be between dial positions 6 and 7.5.

(2).

Modulator plate current may be determined
by observing the increase in total plate current reading
when changing from CW to VOICE and impressing
nbrmal modulation. The modulator plate current
should average 100 to 160 milliamperes for sustained
tones. A greater or smaller value than this indicates
that a readjustment of the input level should be made.

Master-oscillator plate current can be de-

(3).
termined on the total-plate current-meter by remov­ing the p-a and speech-amplifier tubes and placing the
transmitter on CW. The current indicated should
be from 30 to 75 milliamperes, depending on the
transmitter tuning unit in use.

(4).

Power-amplifier plate current may be deter­mined by subtracting from the total plate current on
CW the currents drawn by the master oscillator and

speech amplifier. Its value should be from 100 to 150

milliamperes at full load.

Master-oscillator grid current can be deter-

(5).
mined by connecting a d-c milliammeter in series
with resistor 1109. Correct value should be from 30 to
50 milliamperes.

(6).

Power-amplifier grid current can be deter­mined by inserting a d-c milliammeter in series with
resistor 1112. Correct value is from 15 to 25
milliamperes.

Various other circuits may be checked by referring
to the schematic diagram. Then by referring to the
various unit connection diagrams, the location of the
various circuit elements may be ascertained.

c. Neutralization of Power Amplifier

Neutralization of the power amplifier is not ordi­narily necessary, since this is done when the units are
tested at the manufacturer's plant. However, if the

setting is disturbed for any reason, the following pro-

cedure may be used to restore the adjustment.

The radio transmitter should first be set up and
tuned to see that all power supplies are correct and
the transmitter is functioning properly. Then remove
the power supply cords and the back of the radio
transmitter. From Fig. 2 locate wire 43 (red) on
filter capacitor 1163. Remove this wire with a solder­ing iron and tape clear of terminal on capacitor
1197A. This removes the power-amplifier d-c plate
voltage and leaves the r-f circuits intact. Connect
the vertical plates of a cathode-ray oscillograph to
terminals LOAD A and GND on the radio trans­mitter. Place the ANT. IND. TUNING, M at dial
zero and the ANT. CIRCUIT SWITCH, N on
position 3. Tune the p.a. to resonance as shown by
a maximum amplitude of r-f carrier on the oscillo­graph. Proceed by turning the neutralizing control,
behind the tuning chart, for a minimum amplitude
on the oscillograph, at the same time maintaining
the p.a. in tune. When the best minimum is reached,
with the p.a. in tune, the tuning unit is neutralized.
In the lower frequency tuning units, the oscillograph
pickup will be practically zero at neutralization, while
on the higher frequencies, considerable amplitude
will be noticed from stray ground currents. A check
on the neutralization may be made by noticing the
low reaction on the total plate meter, at neutraliza­tion, as the p.a. is tuned through resonance. The
operator must remove all power plugs, while the

12

transmitter back cover is removed and lead (43)
is resoldered.

d. Dynamotor Unit PE-73-C

(1).

BRUSHES: The brushes can be removed
by unscrewing the slotted ,brush cap on each side of
the bearing bracket. It is recommended that each
brush be suitably marked to indicate which brush
holder it came .from and its relative position in that

brush holder in order that the brushes may later be

replaced in their original positions. THIS IS IM-

PORTANT. Blow out dust and clean all foreign
matter from each brush holder and brush and make
certain that the brushes slide freely in their brush

holders, dressing the brushes with fine sandpaper, or
a file, if necessary. Any brush which has worn down
to a length of less than 3A in. (measured from contact
surface to near end of spring) should be replaced
with new one. In installing new brushes it may be

necessary to "sand-in " the brush in order to make

its contact surface fit the contour of the commu-

tator. The brush must slide freely in its holder.

"Sanding-in" may be accomplished by using a
strip of No. 00 sandpaper about 5 in. by 1 in. for
L.V. brushes and S in. by
Wrap the strip of sandpaper around the commutator
with the sand surface out. Insert the brushes in the
brush holders and replace the brush caps so that
the brushes are pressed tightly against the sandpaper.
Holding the ends of the sandpaper so as to stretch
it tightly against the commutator, rotate the armature

back and forth until the full width of the brush face

is making contact against the sandpaper as indicated

by the sanding marks or scratches on the contact
surface of the brush when it is withdrawn. Sand the
sides of the brush, if necessary, for a free fit in the

holder.

No sanding should be necessary to secure a good
brush fit with the original brushes if they are replaced
correctly. Never apply oil, grease or any other lubri­cant to the brush, commutator or brush holder.
Under normal conditions of operation, it is estimated
that the useful life of brushes is 2000 hours for low­voltage and 10,000 hours for high-voltage brushes.

COMMUTATORS: Both commutators should

(2).
be wiped with a clean, Tintless cloth. Any scum appear­ing on the low-voltage commutator should be removed
by moistening the cloth in carbon tetrachloride.
The normal black or dark brown polished surface
on the high-voltage commutator should not be
removed. The type of brush material used in the
low-voltage brushes of the dynamotor unit may,

under certain conditions of installation, cause a
discoloration of the low-voltage commutator. Under

these circumstances the commutator will have a

mottled appearance which is caused by the formation
of a very thin oxide film on the surface of the commu­tator bars. This film is normal and is not injurious

N

in. for H.V. brushes.

to the commutator or brushes. Do not try to remove
the oxide film described above. A rough or pitted
commutator should be smoothed with No. 00 or finer
sandpaper. Never use emery cloth or a file. Under
normal conditions of operation the low-voltage and
high-voltage commutators should not require turning
down before 2000 hours and 10,000 hours of service
respectively. However, if the commutator bars have

worn down flush with the mica, the armature should
be removed from the dynamotor to turn down the

commutator face and undercut the mica between bars.

(3). BEARINGS: If the armature does not spin
freely when rotated by hand with the brushes re­moved the following may be the cause:

(a)

Dirt or other foreign matter in a bearing.

(b)

Defective ball bearing (cracked race, chipped

or flattened ball) .

(c)

Grease in bearing has become hard and
gummy due to oxidation during long periods
without actual use.
In any case, the armature should be removed from

the frame as described in paragraph 22d (4) and
the bearings thoroughly cleaned. If, after cleaning,
the outer race will not spin smoothly, it is probably
due to a cracked race or chipped or flattened ball,
and the defective bearing should be removed and
replaced with a new one. Always use a bearing puller
to remove a defective bearing and never hammer
or pry the bearing off since this may bend the shaft
and injure the commutator. A new bearing should be
pressed on the shaft until the inner race of the bearing
rests against the shoulder on the shaft. For this
operation always use an arbor press and a metal
cylinder or collar which bears only against the inner
race of the bearing. Care must be taken that no force
or stress is placed on the outer race of either bearing
at any time since this will usually result in a damaged
bearing.

(4). DISASSEMBLY: The following procedure
is recommended for disassembling the dynamotor
unit for cleaning and repacking the bearings:

(a)

Remove the three "safety-wired " screws
on each end of the dynamotor unit and take off the
two end bells.

(b)

Unscrew the slotted brush cap in each brush

holder and remove all four brushes. Take special

care to mark the position of the brushes in their

brush holders such that they may later be replaced
in their exact original positions.

(c)

Unscrew the four slotted screws located
around the rim of the low-voltage bearing bracket
and pry the bracket loose from the frame. The

low-voltage end of the dynamotor unit can be.

identified by the long, small diameter commutator

and the large copper-graphite brushes.

Detach the two field leads from the terminal

(d)

clamps on the low-voltage brush holders by un-

13

screwing the screw in each terminal clamp. It is
not necessary or advisable to remove the terminal
clamp from the brush holders.

(e)

The bearing bracket can now be taken out
of the way and the armature withdrawn from the
frame. Take care not to injure the armature wind­ings or commutator by rubbing against the field
poles. Do not lose any shim washers which may be
in the bearing housings, or which may stick to the
bearing. If any shims are present they must be
reassembled in the same housing.

(f)

End Play Adjustment : A spanner screw is
provided on one bearing bracket for adjusting end

•

play in the dynamotor.. This is properly adjusted
at the factory and ordinarily will not need to be

changed unless the armature is replaced. Before
making any adjustments with this screw, it is
necessary that two setscrews on either side of the
bearing be loosened. Then the spanner screw

should be turned out (counter clockwise) one turn.

Operate the dynamotor until it is hot (about 30
minutes.) The end play should then be adjusted by
turning the spanner screw as required until the
end play as shown on an indicator reading to
1/1000 inch, is between approximately 4/1000 to
8/1000 inch.

In case an indicator is not available an alternative

method of adjusting the end play is as follows:

Screw the spanner screw in until the bearing

starts to growl, then back it off immediately

turn (45 degrees). This latter method must be
used with extreme care since if- the bearings are
set up too tight or allowed to remain tight for any
period of time they may be damaged. The set­screws should then be tightened to hold the spanner
nut in position.

(g)

In cleaning the ball bearings it is not neces­sary to remove them from the armature shaft.
Simply immerse the bearing in a shallow pan of
clean carbon tetrachloride and wash all of the grease

from the bearing. The use of a small camel's-hair
brush will greatly aid the thorough cleaning of the
bearing. Change the cleaning solvent in the pan as
soon as it becomes dirty. Always use clean solvent
for the final rinsing of the bearings.

Do not allow the cleaning solvent to come in

contact with the commutators or windings.

the cleaning fluid is accidentally splashed on these
parts, wipe it off immediately. Make certain the
bearing is thoroughly clean and dry before repack­ing with new grease. If the bearing is not to be
repacked with grease within a few minutes after
cleaning, flush it with a clean, light mineral oil to
protect the polished balls and races from rusting.

(h)

In reassembling the dynamotor unit, follow
in reverse order the procedure for disassembly.
Make certain that the two field leads are securely

attached to the proper terminal clamps on the low­voltage brush holders and that the "slack " or

"loop" in these leads is "tucked" back of the
field coils. Do not loosen or remove the brush
holders from the bearing brackets. If a brush holder
is loosened or removed for any reason, replace it
securely in exactly its original position and check
to make certain the contact surface of the brush
fits the commutator perfectly. If necessary, sand-in
the brush to secure a good fit against the commu­tator.
(5). TYPICAL PERFORMANCE: The dyna-

N3

motor unit alone without the transmitter should
operate approximately as follows on a load test :

Input

Volts

24.0

24.0

24.0

Amperes

5— 7.5
14-16.5
20-22.5

Volts

1140-1160
1070-1090
1025-1050

Note : The input current above includes that

taken by the starting relay.

In case

Output

Milliamperes

0
220
350

14



MICROPHONE CONNECTIONS

14i1

cr,

KEY CONNECTIONS

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NIC. INPUT 011128--MOWN

MC.SIIMTCH OR KEY(T1P)---WMTE

SIDE TONE

KEY RELAY ARM

KEY RELAY BACK—YELLOW
11010,811C.,OR KEY (SLEEVE)—GREEN
03NDONIC..OR KEY (SLEEVE)—BLACK

OK7 SWITCH (DYN. RELAY)

(ON

-

82 2

-

8-8

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p1

1116
1116

1116
1116

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814

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1160

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1117

1172

1127

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TYPICAL TRANSMITTER TUNING UNIT TU

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1183

804

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1108

80 5

1109

1109

1109

1119

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1187

1121

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1110

1122

1197C

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OPT

INTERLOCK OPERATED
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1107

1134

1133

1126

1112

1113

1114

1115

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1135

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1184

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1129

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66

1179

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7,

0

v

4

147

r

i

114 9

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1148

114 5

54

1142

11191

1192

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115 0

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ANTENNA INDUCTAFNCEI

TUNING "M

ANTENNA
CIRCUIT

SWITCH

N"

168

SW2

1169

CAPACITOR

1167

0

ANT

TUNING

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ANT. INDUCTANCE

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1198

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,

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BROWN
YELLOW
GREEN

BLUE
RED
WHITE

ORANGE
BLACK

TO PRIMARY POWER SUPPLY

28 VOLTS DC

TRANSMITTER BC

RADIO

-73-

DYNAMOTOR

UNIT PE

G

Fig. 1. Radio Transmitter BC-375-E, Schematic Diagram

-

375-E

ANTENNA TUNING UNIT BC

-

306-A

Fig. 1

NOTE

WIREMAN SHOULD PLACE WIRE 0 ON !TEM 1163
SUCN TNAT IT MAY SE REMOVED wiTROUT
SEMOYiNG OINER ROMS ON

START

r"

- ;ASTER WIRES SECURELY TO TERMINALS NEGNANICALLY REPOSE

NOTE

SOLDERING USE 110501 CORE SOLDER 82003C

TN E HEAVY LINES
ASSIST IN TRACINGHIGH
NOT NECESSARILY MOIL ATE CAKES

CON DUC OR {H

N 11/704t•

POINTS MA,RNED

•

T
AT POINTS MANSE
AT POINTS 210 NED •2 USE TERMINAL N 78723.6

1170

OU

SAME

TERRIMAL

FINISH —0

WAYS •RE



CONNECTIONS

S



R

USE TERMINAL 1,7872 50•

F USE TERMINAL 18-7S 7020

•



M

I

D

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ON THE

112

LOAD

ANT

-.•

RAREL

116

MIDOL

ISOLAN
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DIAGRAM

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Fig. 2. Radio Transmitter BC-375-E, Connection Diagram

CLEAT MS C•GLE
USE CLEAT N-7453041

71



"`"4,



GREEN

1PLUE

ONE SIDE OF 1103 6401110f 0
SY CONNECTION

20

7

1192

76 30 91—trr

WIRES 60 068
TOM PLACED

RETWEEN

SASSIER

•
MOWN

-11

io

ORANGE

1154

TPA

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1747

IC

O

"

35

SR=

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31

1.16

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EE

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ORANGE

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NE

GREEN

El

ORANGE /SLUE

SLAGS

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GREEN

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LE TOUCHES EDGE 146

C•SE

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-

L

0 

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I A

RISS

NES

TO 110 TERM/SAL Et 2

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CONNECTION

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•

102

-

0

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00,01N COPPER WIRE TINNED

C

0 \ 011.DIA

N i•ANS STRANDS ES/ MEV 1/3E.

E

G

E SPECS N-/97E345

COLORED

IS ISAIAS STRANDS

UNMANNED

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COLORED

UNIT

PIECE OF

N

it 10126 W012630005 V.; BUNSEN INSULATION

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SIZE OF CONDUCTOR

COPPER WIRE TINNED

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Fig.

2

a Low •- TO REMOVE PLUGS

•

OPERATE SIM, SLIDES

WEIGHTS IN POUNDS

•

LLOW TO OPERATE

SNAP-SLIDES

Radio Transmitter BC-375-E,

without Mounting, Transmitter



Tuning Unit, and Tubes

Mounting FT-151-A



49.0

One Set of Tubes, Consisting

of Four Tubes VT-4-C and
One Tube VT-25



Fig. 3. Radio Transmitter BC-375-E, Dimensions and Weights

Transmitter Tuning Unit
Transmitter Tuning Unit
Transmitter Tuning Unit
Transmitter Tuning Unit

3.75
Transmitter Tuning Unit
Transmitter Tuning Unit

2.0

Transmitter Tuning Unit



...

TU-5-B
TU-6-B
TU-7-B
TU-8-B
TU-9-B ...
TU

-

10-B ...

TU-26-B

14.437

12.437

11.687

11.437

11.437

11.437

12.750

5011

TU -5

TU - 6

-

El

-

512 1

1

1500.

-

3000 K C.

8 3000- 4 500 K C

1

"DI

L_

TU - 9 -8

TU

-

10 8





7700

-

10000 K .C.

10000-12500 K C

1021

1054

Fig. 4. Transmitter Tuning Units, TU.-5-B, TU-6-B, TTJ-7-B,

TU-8-B, TU-9-B, TU-10-B, and TU-26-B; Schematic Diagrams

7

11

-

T TTTT

1

-

-

511

NOTE FOR SOLDERING :-

WIRE TO BE FASTENED MECHANICALLY TO
TERMINALS BEFORE SOLDERING. USE ROSIN
CORE SOLDER 820 D3C.

THERE SHALL BE NO SHARP POINTS LEFT
AFTER UNIT IS WIRED EITHER FROM LUMPS
OF SOLDER OR IRREGULARLY CUT WIRE ENDS.

START (BLACK)
TAP*! (BLUE)
TAP*2 ,BROWN)

TA 03 GREEN)
TAP°4 'RED)
TAP*5 !ORANGE),
FINISH (ORANGE /BLACK)

CABLE THESE LEADS.



THESE CAPACITORS LOCATED

UNDER SYMBOL 527

FRONT

527

529

2

VW_ \

T •

25

Ora-

524

523

522

526

521

TOP OF COIL

OF UNIT

NAME

"

• • •

•

•



utlIT PIECE Of APPARATUS

.102 DIA COPPER WIRE TINNED.

MARKED ''X" USE

*

•

• • W"

•

BLOCKING CAPACITOR



CHOKE

•

•



• ^T«

•

^

•

SWITCH

DESCRIPTION

•

z•

•

Y"

•



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•

TERM

^

"

*

• K-

•

• K-

•

•

S"

SOLDER COMPLETE JOINT TOGETHER

V- 14 4 4 4 51

1-78T2217

7872831 C)

71172 366

K

-

78 72306

_

FRONT

50 7

501

TOP

509

I 

T

510

SO

SO

•

516 0

506

515 0

505



514

Q

504

613 0

503

THESE CAPACITORS LOCATED

UNDER SYMBOL 507

SYMBOL

501

M.O. TANK INDUCTANCE
M.O. BAND CHANGE SWITCH

502

M.O. FIXED TANK CAPACITOR

503
504
505
506 • •
507

M.O. VARIABLE TANK CAPACITOR

SOB

P A. GRID CHOKE
509
510

M0 • •
511
512

NEUTRALIZING CAPACITOR

M O. TANK COMPENSATING CAP

5 I 3
514
51S
516 * " 
517

M.O. GRID PARASITIC RESISTOR

321

PA TANK INDUCTANCE

P.A. BAND CHANGE SWITCH

522

P.A. FIXED TANK CAPACITOR

623
524
625

P A. VARIABLE TANK CAPACITOR

527

ANT COUPLING COIL

528
529

CONNECTOR

M

(NOT MARKED

NOTE - AT POINTS

•

•

•

•

l•

• • • 

• • • 

• • 

• • 

• • •

•

• • 

• * 

•

•

•

•

•

S

Fig. 5. Transmitter Tuning Unit TU-5-B, Connection Diagram

-

Tr

E

--

START (BLACK)
TAP*I (BLUE )
TA P *2 kliIROWN)

TAP*3 GREEN)

TAP*4 RED)
TP*5 (ORANGE),

F

INISH (ORANGE/BLACK)

CABLE THESE LEADS

THIS CAPACITOR IS MOUNTED

UNDER SYMBOL 627

Ct

NOTE

6 II

FRONT

827

608



B 61+

ill

5-w

6 I 2

FRONT

607

1

1

01 _II W

.O\

629

622



IX

S

START

TOP \

609

XI

J

X

THIS CAPACITOR LOCATED

UNDER SYMBOL 807

THERE. SHALL BE NO SHARP

UNIT

IS WIRED EITHER FROM LUMPS OF SOLDER
OR IRREGULARLY CUT WIRE ENDS.
WIRE

TO

BE

TERMINALS BEFORE SOLDERING

USE ROSIN CORE SOLDER 820 D3C

SYMBOL

601

602

603

607
608

609

610
611

812

613
114

621
622
623

627
628

629

co“..m.

M

gr

'acca

FASTENED MECHANICALLY TO

NAME OF UNIT

MO TANK INDUCTANCE
MO BAND CHANGE SWITCH
MO FIXED TANK CAPACITOR

MO VARIABLE TANK CAPACITOR
PA GRID CHOKE
PA GRID BLOCKING CAPACITOR
MO GRID BLOCKING CAPACITOR
MO GRID CHOKE
NEUTRALIZING CAPACITOR

MO COMPENSATING CAPACITOR

PkGRID PARASITIC RESISTOR

PA TANK INDUCTANCE

PA BAND CHANGE SWITCH
PA FIXED TANK CAPACITOR

PA VARIABLE TANK CAPACITOR
ANTENNA COUPLING COIL

ANTENNA COUPLING SWITCH

SIZE OF CONNECTOR

UNIT PIECE OF APPARATUS

.102 DIA COPPER WIRE TINNED

POINTS LEFT AFTER

S

0

TOP OF COIL

Fig.

6.

Transmitter Tuning Unit TU-6-B, Connection Diagram

NOTE' AT POINTS MARKED" X" USE TERM V

" E"



•

" W "



" S " SOLDER COMPLETE JOINT TOGETHER

-

K

-

K

-

K

-

1444451
7872305
787 2 831

7872368

0

r1,771

-

4A-J

NOTE.

AT POINTS MARK110"5" USE TERM. V-1444451

61



II



"



" "



•





K-71372 3 05

K-78 72 8 31 W

"



IC-7117 2 31313

• 7"

Id •



-

171-1- 



-

1717171

-

17

1-



• •

v

, 11.

" 5" SOLDER COMPLETE JOINT TOGETHER

START (BLACK)

TAPS 1 (SLUE)
TAN E (BROWN)
TAPIA (GREEN)
TAPP,.



TAFT'S (ORANGE)

FINISH (ORANOEH1LAOK)

)

704

705

TOP

707

722



723

NOTE:.

THERE SHALL SE NO SHARP POINTS
LEFT AFTER UNIT IS WIRED EITHER
FROM LUMPS OF SOLDER OR IRREGULARLY
CUT WIRE ENOS.

WIRE TO BE FASTENED MECHANICALLY TO
TERMINALS BEFORE SOLDERING USE ROSIN

CORE SOLDER 520D38

SYMBOL
UN 17.7

701
702
703
704
706
706
707

721
722

723
724

CONNECTION

14

NN IEI)

NAME OF UNIT

MD.TANK INDUCTANCE
MA TANK CAPACITOR
MA GRID BLOCKING CAPACITOR

MA GRID CHOKE

PA.GRIO BLOCKING CAPACITOR
P.A. GRID CHOKE
NEUTRALIZING CAPACITOR

R A TANK INDUCTANCE
RA TANK CAPACITOR

ANT. COUPLING CO)L

ANT COUPLING SWITCH

SIZE OF CONNECTOR

SPECIFIED ON MECHANICAL DRAWING
COPPER WIRE TIMM( .102 01A.

•

)

Fig. 7. Transmitter Tuning Unit TU-7-B, Connection Diagram





NOTE.

AT POINTS MARKED"X " USE TERM. V-1444451

I. II



Y"



" W"



" S" SOLDER COMPLETE JOINT TOGETHER

K-7872305

K-7872831 0
K-7872368



(BLACK) --44

TARSI (SLUE)

TARR 2 (BROWN)

TAROS (GREEN)

TAP04 (RED )
TAROS (ORANGE)
FINISH (ORANGE/BLACK)





FRONT



3. :4
803

8,13

FRONT

NOTE

THERE SHALL BE NO SHARP POINTS LEFT AFTER UNIT
IS WIRED EITHER FROM LUMPS OF SOLDER OR
IRREGULARLY CUT WIRE ENDS

WIRE TO BE FASTENED MECHANICALLY TO

TERMINALS BEFORE SOLDERING USE ROSIN

CORE SOLDER 820038

SYMBOL

4

r8

UNIT

801

802

803

804
805

808

807

8 2 I
822
823

824

CONNECTION

M

MR;ED

NAME OF UNIT

MD. TANK INDUCTANCE
MO TANK CAPACITOR
M.O. GRID BLOCKING CAPACITOR

MO GRID CHOKE

PA. GRID BLOCKING CAPACITOR

PA GRID CHOKE

NEUTRALIZING CAPACITOR

PA TANK INDUCTANCE
PA.TANK CAPACITOR
ANT COUPLING COIL

ANT COUPLING SWITCH

SIZE OF CONNECTOR

SPECIFIED ON MECHANICAL DRAWING
COPPER WI RE TI NNE 0 .102 DIA

821

Fig. 8. Transmitter Tuning Unit TU-8-B, Connection Diagram

FTTTITT7

-1:-

NOTE:

AT POINTS MARKED"X " USE TERM.

•

Y"

" W "

• • 

• " S " SOLDER COMPLETE JOINT TOGETHER

V-1444451

7872305

K

-

•
K-7137213310
K-7672568

"

.

NOTE:-

THERE SHALL BE NO SHARP POINTS LEFT

AFTER UNIT IS WIRED EITHER FROM LUMPS

OF 10,Pki OR IRREGULARLY CUT

WIRe en

WIRE TO

TERMINALS BEFORE SOLDERING USE ROSIN
CORE SOLDER B20038

FASTENED MECHANICALLY TO



START (BLACK)
TAP*, (BLUE)

TAP*2 (BROWN)

TAP•3 (GREEN)

TAPW4 (RED)
TAP•5 (ORANGE
FINISH (ORANGE/BLAF*

:FRONT

FINISH

922

923

921

905

TOP

903

909

--s\ BOTTOM END OF THIS
CAPACITOR GROUNDED

BY "M" CONNECTION.

FINISH

902

FRONT

901

SYMBOL

UN1T*9

901
902

II

903
904
905
906

907

909

9 2 I
9 2 2
923

924

CONNECTION



M

MARKED

NAME OF UNIT

M.Q. TANK INDUCTANCE
MO TANK CAPACITOR
M 0 GRID BLOCKING CAPACITOR
MO GRID CHOKE

GRID BLOCKING CAPACITOR

PA


PA GRID CHOKE
NEUTRALIZING CAPACITOR

M.0 BY PASS CAPACITOR

PA.TANK INDUCTANCE
PA TANK CAPACITOR
ANT COUPLING COIL

ANT COUPLING SWITCH



SPECIFIED ON MECHANICAL DRAWING

COPPER WIRE TINNED 102 DIA

SIZE OF CONNECTOR

Fig. 9. Transmitter Tuning Unit TU-9-B, Connection Diagram

.LL

-

Tr

•

NOTE,

AT POINTS MARKED " X " USE TERM. V-1444 4 SI



---r

.1 I.

NOTE:-

THERE SHALL BE NO SHARP POINTS
LEFT AFTER UNIT IS WIRED EITHER
FROM LUMPS OF SOLDER OR IRREGULARLY

CUT vim ENDS.
WIRE TO OE FASTENED MECHANICALLY TO

TERMINALS BEFORE SOLDERING USE ROSIN
CORE SOLDER 820038

"

•

Z "

••

^

•

y“

•



•

•

• •

"

W

"

• S "SOLDER COMPLETE JOINT TOGETHER

•

7872305

K

-

7872 83 1 (2)

K

-

7012368

START (BLACK)
TAPS (BLUE)

TAPS I (BROWN)

TAP• 3 (GREEN)

TAPS. (no )
TAP• 5 (ORANGE)

FINISH (OR ANGEIBLACK)

)

1022

10 21

FINISH

1010

100 5

TOP

BO T TOM END OF THIS
CAPACITOR GROUNDED
BY" M CONNECTION

1002

T

FRONT

1001

FINISH

SYMBOL

UN IT*IO

1001
1002
1003
1004

1005
1006
1001

1009
1010

1021
1022
1023
1024

CONNECTION

MAR KEO

NAME OF UNIT

MO TANK INDUCTANCE

M 0 TANK CAPACITOR
M.O. GRID BLOCKING CAPACITOR
M.O.GRIO CHOKE
PA GRID @LOCKING CAPACITOR

P.A GRID CHOKE

NEUTRALIZING CAPACITOR

M.0 BY PASS CONDENSER
MO. CHOKE

PA TANK INDUCTANCE
PA TANK CAPACITOR
ANT COUPLING COIL
ANT COUPLING SWITCH



SPECIFIED ON MECHANICAL. DRAWING

COPPER WI RE TI NNE D .102 DIA

SIZE OF CONNECTOR

Fig. 10. Transmitter Tuning Unit TU-10-B, Connection Diagram

NOTE FOR SOLDERING-

WIRE TO BE FASTENED MECHANICALLY TO TERMINALS
BEFORE SOLDERING USE ROSIN CORE SOLDER 820036

LEFT AFTER UNIT IS WIRED EITHER FROM LUMPS OF
SOLDER OR I RREGULARY GUT WIRE ENDS

THERE SHALL BE NO SHARP POINTS

SYMBOL

2601
2602
2603
2604
2605

2606
2607
2608
2609
2610
2611
2612

-

2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2627
2628

CONNECTOR

M

NOT MARKED

NAME OF PART

M 0 TANK INDUCTANCE
MO PLATE CHOKE
M.0 GRID CHOKE
M 0 GRID BLOCKING CAPACITOR
M 0. TANK COMPENSATING CAP
PA GRID CHOKE
MO BAND CHANGE SWITCH
M 0. FIXED TANK CAPACITOR
MO FIXED TANK CAPACITOR
M CI CHAIN CAPACITOR
MO CHAIN CAPACITOR

M 0 CHAIN CAPACITOR

M 0 CHAIN CAPACITOR
M 0 CHAIN CAPACITOR
M 0 CHAIN CAPACITOR
NEUTRALIZING CAPACITOR
MO GRID PARASITIC RESISTOR
P.A. GRID BLOCKING CAPACITOR
MO. TANK COMPENSATING GAP
MO TANK COMPENSATING CAP
P.A TANK INDUCTANCE
PA BAND CHANGE SWITCH
PA FIXED TANK CAPACITOR
PA FIXED TANK CAPACITOR
PA FIXED TANK CAPACITOR
ANT COUPLING COIL
ANT COUPLING SWITCH

UNIT PIECE OF APPARATUS
.102" DIA COPPER WIRE TINNED

DESCRIPTION

Fig. 11. Transmitter Tuning Unit TU-26-B, Connection Diagram

NOTE- AT POINTS MARKEVS "SOLDER COMPLETE JOINT TOGETHER

AT POINTS MARKED"T" USE TERM ht-7872305

AT POINTS MARKED"W" USE TERM K-7872368

AT POINTS MARKED"X "USE TERM V-1444451

AT POINTS MARKED"Z" USE TERM K-7870226

AT POINTS MARKED"N" TERMINALS CALLED FOR ON

AT POINTS MARKEO"Y" USE TERM V-1451309

MECANICAL DRAWING

A

0

0

NAME
PLATE

311

t13 —

4

0

O

Weight of Case CS-48

Fig. 12. Case CS-48, Dimensions and Weights

f



0..



4.375 lb

BOTTOM END OF THIS CAPACITOR
GROUNDED BY • M 'CONNECTION.

RED

C • - Y

SLACK—ft.

0

A

6.

.r

„

. ,...,,,

1

608_

Jr •

M

7

4,

, \

s ' - ....%

t





r

I ., / 760

y

I

-4--165,

b



1618

r

ei--______i

731'

NOTE:- CUT ALL LEADS TO PROPER LENGTH SUCH THAT THEY

TAKE THE POSITIONS SHOWN IN CONNECTION DIAGRAM
WHEN TERMINAL BOARD IS SECURED IN PLACE

TO PREVENT EXTERNAL BRAID OF "B" CONNECTIONS FROM

1610

FRAYING. ASSEMBLE CAP K.78
EACH LEAD BEFORE SOLDERING TO TERMINAL

REMOVE METAL IDENTIFICATION TAGS FROM THE FOUR
DYNAMOTOR LEADS AFTER CONNECTIONS ARE MADE.

76

3 91 TO RELAY END OF

A

<EEN

CONNECTION

- I

SIZE OF CONDUCTOR

A
ST
C

IA
2

0400IA COPPER WIRE TINNED

A SAWS S 1-12249

*16AWS

0

4

*14AWG i RUBBER INSULATION K-7972345
UNIT



PIECE OF APPARATUS

*MARC& RUBBER INSULATION (RED) II- 7571345, PT

(BLACK)

RUBBER INSULATION K • 7012345

I--

'

-

y

CONNECTION

X

Z
W
S

-

II

T
R

TERMINAL

K-787283I
V-418575
K-7170965 PT-2

V-I



V-41759I

8-1450158
K-7975873

Ir. -1:

38

SCREW ON BRUSH

END OF DYNAMOTOR



RIGGING

HIGH VOLTAGE

BRUSH HOLDER SCREW





LOW VOLTAGE

END OF DYNAMOTOR

Fig. 13. Dynamotor Unit PE-73-C, Connection Diagram



4





PI. - SI

TRANS



NAME

'4101

I

0

a:,

I



PL -59

ALLOW 4" TO REMOVE

PLUGS H TO OPERATE

SNAP- SLIDES



3

fiSiV:T1

' TO

O
SNAP-SLIDES

17*

6- ra- DIA MOUNTING

HOLES 3 HOLES LOCATED
ON EACH END OF MOUNTING
PLATE

a

L1 LI

4

,

0

I



“Ik

Weight of Dynamotor Unit PE-73-C Less Mounting

412

MOUNTING

FT-107



Weight of Mounting FT-107

Fig. 14. Dynamotor Unit PE-73-C, Dimensions and Weights

2i.

37.25 lb

... 1.45 lb

NEXT TO PANEL

1501

swl

ANT

B

TRANS.

A

GND.

TOP

1502

ROTOR

A

014061

REAR VIEW

CONNECTION

UNMARKED

A

AT POINTS MARKED 'X" USE COTTER PIN it x

SIZE OF CONDUCTOR

.10e DIA . COPPER WIRE TINNED
.080' DIA. COPPERWIRE TINNED

I

Fig. 15. Antenna Tuning Unit BC-306-A, Connection Diagram

6

GND 

RANS

A

ANT

MOUNTING
FT-142

9

Weight of Antenna Tuning Unit

BC-306-A Less Mounting

Weight of Mounting FT-142





9.062 lb

0.687 lb

Fig. 16. Antenna Tuning Unit BC-306-A, Dimensions and Weights

6'

4 MOUNTING HOLES

FORKS FL HD SCREWS

2 MOUNTING HOLES
FOR * 10 SCREWS.

.257" DIA.

HOLE

Weight of Mounting FT-115-B



0.195 lb

I

"

16



II"

16



1

52.

ip







16

•

2

Fig. 17. Mounting FT-115-B, Dimensions and Weight