RCA Radiola 16 Operating and maintenance manual

RCA
Radiola 16
SERVICE NOTES
1(('A Radiola 16
Third Edition -10M -January. 1929
Radio Corporation of America
233 BROADWAY, NEW YORK CITY
DISTRICT SERVICE STATIONS
BROOKLYN, N. Y. CHICAGO, ILL. SAN FRANCISCO, CAL.
Bld. No. 19-168 - 39th. St. 2001 West Pershing Road 274 Brannan St.
DALLAS, TEX. ATLANTA, GA.
Santa' Fe Bldg., Unit No. 2 Monroe Bonded Warehouse, Spring and Peters Sts.
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A WORD OR TWO ABOUT SERVICE
Service goes hand in hand with sales. The well-informed RCA Authorized Dealer renders
service at time of sale in affording information as to proper installation and upkeep. Subse-
quent service and repair may be required by reason of wear and tear and mishandling, to the
end that RCA Loudspeaker and Radiola owners may be entirely satisfied.
Obviously, this service can best be rendered by properly equipped service organizations
having a thoroughly trained personnel with a knowledge of the design and operation of RCA
Loudspeakers and Radiolas.
Such service organizations have been established by RCA Distributors, and RCA Authorized
Dealers are advised to refer any major work or replacement to their selected Distributors.
Minor replacements and mechanical and electrical adjustments may be undertaken by the RCA
Dealer.
To assist in promoting this phase of the Dealer and Distributor's business the RCA
Service Division has prepared a series of Service Notes-of which this booklet is a part
containing technical information and practical helps in servicing RCA Loudspeakers and
Radiolas.
This information has been compiled from experience with RCA Dealers and Distributors'
service problems and presents the best practice in dealing with them. A careful reading of these
Service Notes will establish their value, and it is suggested they be preserved for ready
reference.
In addition to suppl) ing the Service Notes, the RCA Service Division maintains a corps of
engineers who are qualified to render valuable help in solving service problems. These engi-
neers call upon the trade at frequent intervals to advise and assist RCA Distributors in the
performance of service work.
Property of Radio Corporation of America. Con fdentla! and to he used only by its
authorized distributors and dealers in furnishing service iv connection with its apparatus.
Copyright 1929-Radio Corporation of .4nzerica.
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CONTENTS
A Word or Two About Service -
Introduction -
Page25
PART I-SERVICE DATA
Radiotron Sequence -
Circuit Characteristics - - - 6
Antenna Installation (Outdoor Type) 6
Antenna Installation (Indoor Type) - 7
Ground - -
Antenna System Failures
Radiotron Sockets - 8
Radiotron Prongs . - 8
Loose Volume Control Contact - 9
Adjustment for Slack Drum Cable 9
Tuning Knob Loose - - - 10
Broken Cable - - - - -
Using Radiola 16 With RCA "B" Battery Eliminator or Similar Devices 10
Not Supplying 67 Volts Plate Voltage - - - - 11
Loudspeaker Polarity - - - - - - - - 12
Uncontrolled Oscillations - - - - - - - - - 12
Audio Howl - - - - - - - _ - - - 13
Distorted Reproduction - - - - - - - - - - 13
Acoustic Howl - - - - - - - - - - 13
Battery Cable - - - - - - - - - - - 14
Refinishing Marred Surfaces - - - - - - - 14
Continuity Tests - - - - - _ - 14
Continuity Test Chart - - - - - - - - 15
Important Precautions - - - 15
Service Data Chart - - - - - - - - 20
PART II-MAKING REPLACEMENTS
Replacing Antenna Coil - - - - 16
Replacing Radio Frequency Coils - - 16
Replacing Gang Sockets - 17
Replacing Main Timing Condensers and Drive 18
Replacing Large By-pass Condensers 18
Replacing Audio Transformers - 19
Replacing Condenser Drive Cable - 19
Replacing Dial Scale - - 19
ILLUSTRATIONS
RCA Radiola 16 - - - - - - - 1
Top View of Chassis Assembly - - - - - 4
Radiotron Sequence - - - 5
Three-Gang Condenser Cable Adjustment - - - 7
Three-Gang Condenser Cable and Drum Mechanism - - - 9
Schematic Circuit of RCA Radiola 16 - - - - - - - 10-11
Resistance Measurement Circuit - - - - - - - - 13
Filament Polarity - - - - - 14
Removing Chassis from Cabinet - - - - 16
Sub-Chassis Assembly - - - - - - - 17
Audio Frequency Transformer Color Scheme of Connections - - 18
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RCA RADIOLA 16
SERVICE NOTES
Prepared by
RCA SERVICE DIVISION
INTRODUCTION
RCA Radiola 16 is a tuned radio frequency receiver employing five Radiotrons
UX-201A and one Radiotron Uri-112A. The tuning range of Radiola 16 extends from
550 to 1400 Kilocycles or 546 to 214 meters approximately. This amply covers the
broadcast band of wavelengths. The utmost in simplified tuning is provided by having
but two controls, one for the selection of stations and one for the adjustment of volume.
Radiola 16 is designed to operate without the use of vernier tuning condensers or adjust-
able rheostats. Excellent quality of reproduction is obtained by the use of properly
designed audio transformers and a power amplifier Radiotron easily capable of handling
the signal delivered to the last audio, amplifier.
Service work in conjunction with RCA Radiola 16 should be small, since all construc-
tion is of a simple character (See Figure 1) and of fool-proof design. However, for the
guidance of those called upon to locate and remedy any trouble that may occur the
following notes are presented.PART I-SERVICE DATA
(1) RADIOTRON SEQUENCE
Figure 2 illustrates the sequence of the Radiotrons as applied to the path of the
incoming signal. From right to left when facing the front of the Radiola, the Radiotron
sequence is as follows:
Radiotron No. 1 is an untuned stage of radio frequency amplification. It is coupled
directly to the antenna and ground and is not tuned in any way.
2ND
A.F.
TO LOUDSPEAKER..
ISTA.F. DETECTOR gRo
R. F.
Zwo
R. F.
1ADIO FREQUENCY -
AUDIO FREQUENCY
TO ANTENNA
1sTR.F.
Figure 2-Radiotron sequence in RCA Radiola 16
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Radiotron No. 2 is a stage of tuned R. F. amplification employing a grid resistance
to prevent oscillation. It is tuned by means of the first of the three-gang condensers. .
Radiotron No. 3 is the second stage of tuned R. F. amplification. It also employs a
grid resistance for the purpose of stabilizing or preventing self oscillation in the circuit.
It is tuned by the second of the main tuning condensers.
Radiotron No. 4 is the tuned detector. This circuit employs a tapped resistance
across the filament leads for the purpose of improving tone quality.
Radiotrons No. 5 and No. 6 are respectively the first and second stages of audio
frequency amplification. The last stage, Radiotron No. 6, employs power amplifier
Radiotron U$.-112A.
(2) CIRCUIT CHARACTERISTICS
The following principles are incorporated in the circuit design of Radiola 16.
1. A three-gang condenser, employed to tune two radio frequency and the detector
circuits, provides one tuning control.
2. An aperiodic antenna circuit, or 1st R. F. circuit, eliminates the necessity for a
separate antenna tuning control or a vernier across the antenna tuning condenser.
3. A plate voltage of 67 volts is used ;on all radio frequency stages without a "C"
battery. This provides simplicity in battery circuits without any loss of sensitivity or
tone quality.
4. The volume control regulates the filament voltage of the three radio frequency
amplifiers. This gives a smooth control of volume with minimum distortion.
5. No neutralizing condensers are employed. Grid resistances in the radio frequency
amplifier circuit effectively prevent any self oscillation that might occur. This is a
simple and effective method of overcoming any oscillating tendency of the radio frequency
amplifiers.
6. A fixed resistor is used in the filament circuit instead of a variable rheostat. This
eliminates an extra control on the panel and safeguards the filaments of the Radiotrons
against excessive voltage.
7. A plate voltage of 135 volts is used on both audio stages in conjunction with a
negative grid bias of 9 volts. This simplifies battery connections and provides a more
uniform drain on the "B" batteries. Also more amplification is obtained in the first audio
frequency stage, which, when used with power amplifier Radiotron UX-112A in the second
stage, results in greater volume with minimum distortion delivered to the loudspeaker.
These various circuit characteristics of Radiola 16 are all of a nature that provides
the utmost in simplicity consistent with good performance and tone quality. The appear-
ance of the set is in line with its internal mechanism.
(3) ANTENNA INSTALLATION (Outdoor Type)
The most efficient antenna system for Radiola 16 is one of 25 to 75 feet in length-
depending upon local conditions-measured from the far end of the antenna to the ground
connection. It should be erected as high as can be conveniently arranged and as far
removed from all obstructions as possible. The lead-in should preferably be a continua-
tion of the antenna itself, thus avoiding all splices which introduce additional resistance
to the antenna system and which may in time corrode sufficiently to seriously affect
reception. If, however, it is absolutely necessary to splice the lead-in to the antenna, the
joint must be carefully soldered to insure a good electrical contact. Excess flux should be
cleaned off and the connection carefully covered with rubber tape to protect it from the
oxidation effects of the atmosphere.
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The antenna and lead-in should be supported by high grade glass or porcelain in-
sulators. At no point should the antenna or lead-in wire come in contact with any part
of the building. The lead-in wire should be brought through the wall or window frame and
insulated therefrom by a porcelain tube.
The antenna should not cross either over or under any electric light, traction or
power line and should be at right angles to these lines and other antenna. It is desirable
to keep the lead-in a foot or more from the building where possible. When an outdoor
antenna is used it should be protected by means of an approved lightning arrestor, in
accordance with the requirements of the National Fire Underwriters' Code.
Figure 3-Turning the cable adjusting screw to take up slack in condenser control cable
(4) ANTENNA INSTALLATION (Indoor Type)
Where the installation of an outdoor antenna is not practical, satisfactory results
may be had by using an indoor antenna consisting of about 50 feet of insulated wire
strung around the picture molding. The size of the wire is not particularly important,
though No. 18 B. & S. bell wire is suggested. In buildings where metal lathing is employed,
satisfactory results are not always possible with this type of antenna. Under such condi-
tions, various arrangements of the indoor antenna should be tried to secure satisfactory
results. An indoor antenna is not as efficient as a properly installed outdoor antenna.
(5) GROUND
A good ground is quite as important as the antenna. No specific recommendations
can be given in this matter as conditions vary in different locations. Water and steam
pipes usually make good grounds. Gas pipes usually make poor grounds, and as a rule
are to be avoided. If neither water nor steam pipes are available, a pipe or metal rod
may be driven into the ground to a depth of several feet. The success of this type of
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ground depends upon the moisture present in the soil. The ground lead should be con-
nected by means of an approved ground clamp to a section of pipe that has been scraped
and thoroughly cleaned. The connection should be inspected from time to time to make
certain that a clean and tight electrical contact exists between the clamp and pipe.
It is recommended that the service man experiment with various grounds, and employ
the one giving the best results. Radiola 16 is capable of receiving over good distances
when connected to an efficient antenna and a low resistance ground. A poor ground
connection may not be apparent on local reception, but it is an important factor in distant
reception and it may also cause oscillation.
If the results of experiments seem to indicate that a good ground connection is not
possible, the use of a counterpoise is suggested if local conditions permit. A counterpoise
is in effect a second antenna. It should be about six feet above ground, well insulated, of
the same dimensions as the antenna and located directly under it. The counterpoise is
connected to the Radiola in place of the ground connection.
(6) ANTENNA SYSTEM FAILURES
Complaints of swinging signals, or of intermittent reception with probable grating
noises, as distinguished from fading effects, are generally the result of antenna and
ground system failures and to this, therefore, the serviceman should give his first attention.
A grating noise may be caused by a poor battery connection, a poor lead-in connection
to the antenna, or antenna touching some metallic surface, such as the edge of a tin roof,
drain pipe, etc. By disconnecting the antenna and ground leads from Radiola 16 and
noting whether or not the grating continues, the service man can soon determine whether
or not the cause of complaint is within or external to the receiver and plan his service
work accordingly.
(7) RADIOTRON SOCKETS
The sockets in Radiola 16 are of the standard gang UX type. The three-gang
socket is fer the radio frequency amplifiers; the single socket is a cushioned socket for
the detector and the two-gang socket is for the audio frequency amplifiers. Care must be
exercised when inserting Radiotrons in the sockets. A socket contact may not be in its
correct position and forced insertion of a tube will bend or break it. If care is exercised
and the Radiotron inserted gently, little trouble will be experienced with socket contacts.
A bent one will be noticeable on inspection and may be corrected by inserting a narrow
instrument in the socket hole and pushing the contact into its correct position. A badly
bent or broken socket contact must be replaced.
(8) RADIOTRON PRONGS
Dirty Radiotron prongs may cause noisy operation. They should be cleaned oc-
casionally with a piece of fine sand paper. The use of emery cloth or steel wool is not
recommended. Before re-inserting Radiotrons in the sockets, wipe the prongs and base
carefully to make certain that all particles of sand are removed.
In placing Radiotrons in the gang sockets care should be exercised to make certain
that the two large pins and two small pins of the Radiotrons match the socket holes.
If a Radiotron will not fit into a socket without considerable pressure being applied, the
trouble is probably due to excessive solder on one or more of the prongs. This may be
removed with a file or knife. Never try to force one in. These sockets are so designed
that the prongs of the Radiotrons will fit in snugly without force being applied. If
sufficient force is applied it might be possible to insert the prongs in the wrong holes,
resulting in a filament burnout.
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(9) LOOSE VOLUME CONTROL CONTACT
A loose volume control contact may cause noisy or intermittent operation and should
be remedied. If the contact arm is loose, the remedy is to bend it slightly so that it makes
firm contact against the resistance strip. In order to do this it is necessary to remove
the chassis from the cabinet as described in Part II, Sec. 1. The volume control is then
readily accessible. By removing the two screws that hold it to the metal frame it may be
completely removed. After adjusting the contact, replace the mounting screws and return
the chassis to the cabinet. Replace screws and control knobs.
MAXIMUM ADJUSTMENT OF
CABLE ADJUSTING SCREW
iI
wi
NORMAL POSITION'''
OF CABLE
CABLE ADJUSTING SCREW
REMOVED TO ALLOW HALF-TURN
EXTENSION OF CABLE ON DRUM
DOTTED LINES INDICATE REVERSAL
OF PIN AND HALF -TURN EXTENSION
eF CABLE ON DRUM
Figure 4-Three-gang condenser cable and drum operating mechanism
(10) ADJUSTMENT FOR SLACK DRUM CABLE
The main tuning condensers are controlled by a cable and drum arrangement giving a
smoothly acting vernier movement that has no back lash. See Figure 1.
After considerable wear, or extreme changes of temperature the cable may become
slack. To take up this slack open lid of cabinet and turn the cable. adjusting screw
with clamp until the cable is taut-See Figure 3. In extreme cases as might occur after
considerable use and several adjustments this screw may become seated thus allowing no
further tightening of the cable. When this condition occurs it will be necessary to slip
the cable a half turn on the grooved drum. To make this adjustment it is necessary to
remove the chassis from the cabinet as described in Part II Section 1. Remove the cable
adjusting screw and Clamp-See Figure 4. The cable will then have approximately one
inch slack. By removing the tapered pin holding the front grooved drum to its shaft and re-
placing it on the opposite s_de (180 degrees) the one-inch slack in the cable can be taken
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up by using the new position of the pin for anchoring the cable. Figure 4 illustrates this
operation. It will be noted that the tapered pin in the new position cannot be inserted as
far as originally. However it can be inserted far enough to lock the grooved drum to the
control shaft and clear the metal housing. If the cable again is stretched to the maximum
adjustment of the cable adjusting screw the tapered pin can be returned to its original
position and a half turn slipped on the drum which will provide for taking up all slack.
Sufficient grooves are provided on the drum for this purpose.
(11) TUNING KNOB LOOSE
If the panel control knob becomes loose on the shaft, tighten the small set screw that
holds the knob to the shaft or if its threads are defective, replace the knob.
2' R. F. GRID aro R.F. GRID
RESISTANCE') RESISTANCES;
800 OHMS ;' 600 OHMS.3
o
GANG CONDENSERS VOLUME
CONTROL
GROUND TO FRAME
(12) BROKEN CABLE
Should a cable become broken due to considerable use or excessive tightening, the
proper remedy is to replace the cable. The procedure for making this replacement is
described in Part II, Section 7. However if a new cable is not immediately available a
temporary repair may be made in the following manner provided the break in the cable is
not in that section that passes over the small grooved drums.
The two ends should be spliced together and then soldered. Splicing consists of inter-
weaving the strands as with rope and not just twisting the cable ends together as in an
electrical wiring splice. Splicing gives greater strength and results in a smaller body
being formed on the cable. When soldering, use plenty of flux and a small amount of
solder. Heat sufficiently long for the solder to adhere to all the small strands of the
DETECTOR. GRID
CONDENSER;
Figure 5-Schematic circuit diagram of RCA Radiola 16
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cable. Placing the splice in an alcohol or bunsen flame affords sufficient heat and allows
any excess solder to drip away. It is to be understood that this is but a temporary
repair and should be used only until a new cable can be procured and installed.
(13) USING RADIOLA 16 WITH RCA "B" BATTERY ELYMINA-
TOR OR SIMILAR DEVICES NOT SUPPLYING 67 VOLTS
PLATE VOLTAGE
Radiola 16 uses a.plate voltage of 67 volts for the radio frequency amplifiers and it
is important that this voltage is not exceeded. (See Figure 5). A higher voltage may
cause it to oscillate and in all cases seriously affect its tone quality. It is imperative that,
when using "B" battery eliminators having fixed 90-volt taps, provision be made for
GRID
LEAK
BY PASS:'
CONDENSER
OUTPUT
o 13+135..... RED
A+A-
-4_,,O+B- }...
SWITCH=' GND
FILAMENT
RESISTOR;W
BY -PASS;'
CONDENSER DETECTOR
TAPPED
RESISTOR
YELLOW
BLACK WITH
YELLOW TRACER
GREEN WITH
RED AND
BLUE TRACER
O 8+67MAROON & LED
o B+45MAROON
l c 9 BLACK WITH
GREEN TRACER,
and wiring color scheme for making battery connections
reducing them to 67 volts. Off hand it would seem that a series resistance could be used
to drop the voltage, but when we realize the plate voltage varies in practically all of these
devices except in the case of the RCA "B" Eliminator (Duo-Rectron) and similar devices
a fixed resistor would give a varying voltage depending on the device.
A potentiometer having sufficiently high resistance (at least 18,000 ohms) shunt-
ed across the +45V and +90V taps with the contact arm connected to the 67-volt lead
from the receiver will give a variable voltage between 45 and 90 volts for this lead. By
taking a high resistance voltmeter and connecting from -B to this arm, it may be ad-
justed for 67 volts. A drop of solder will make a permanent connection between the arm
and resistance element and prevent a possible change in voltage. The General Radio
Potentiometer No. 371 (18,000 ohms) is recommended for this purpose.
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(14) LOUDSPEAKER POLARITY
In Radiolas employing Radiotron UX-112A in thelast audio amplification stage it
is very important to have the loudspeaker so connected that the magnetic field generated
by the relatively large plate current from the 135-volt B battery will not oppose the per-
manent magnetic field of the speaker pole pieces. In Radiola loudspeakers of the horn
type the solid brown lead should be connected to the left jack when facing the front of
Radiola 16 and the black lead with brown tracer to the right jack. If speakers, similar
to the UZ-1325, are incorrectly connected they will soon lose their sensitivity through a
weakening of the permanent magnetism of the pole pieces. When the leads are properly
connected, the magnetic field generated by the steady plate current in the speaker coils
intensifies the permanent magnetic field -of the pole pieces and maintains the permanent
magnetism.
If there is doubt of the correct connection, loudspeakers with metallic diaphragms
such as UZ-1325 should be so adjusted that the diaphragm just strikes the actuating
magnets or pole pieces as will be evidenced by a clattering noise when loudest notes are
played. Reversing the loudspeaker leads will either accentuate or lessen the clattering.
That connection which gives greatest clattering is the correct one to use. The speaker
should then be readjusted so that no clattering occurs on the greatest volume desired.
In RCA Loudspeakers Models 100, 100A, 102 and 104 however, the polarity is not
an important factor. They should accordingly be connected in the manner that gives
the most pleasing reproduction.
(15) UNCONTROLLED OSCILLATIONS
Should Radiola 16 oscillate or regenerate at any point in the tuning range the
trouble is probably caused by-
1. Excessive plate voltage on the R. F. or detector tubes.
2. Excessive filament voltage.
3. Defective grid resistor in 2nd R. F. or 3rd R. F. (Figure 5).
The remedy in the case of No. 1 or No. 2 is to reduce the plate or filament voltages
to their correct value. Excessive voltage on the radio frequency amplifying tubes will
also cause distorted reproduction from the Radiola.
In the case of No. 3 the various grid resistances in Radiola 16 may be checked by
means of a resistance bridge. If a resistance bridge is not available the voltmeter-am-
meter method gives accurate results provided the meters used are calibrated accurately.
This method makes use of. a milliammeter with a scale of 0-25 and a voltmeter of 0-7
volts. A voltage is then applied that will give a substantial reading. A circuit diagram
of this method is shown in Figure 6.
The resistance may then' be calculated by the use of Ohms law.
E
R = -(Where R equals ohms, E equals volts and I equals amperes)
I
or 1000 Volts
Milliamperes 1
Since the current reading is taken in milliamperes (or ampere) it is necessary
1000
to multiply by 1000 to get the resistance value in ohms.
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The values of the various resistances are shown in the schematic diagram Figure 5.
In some cases with certain antennas, the Radiola may oscillate even though every-
thing is O. K. The remedy in this case is to interchange the Radiotrons or to reduce the
volume control a slight amount.
(16) AUDIO HOWL
An audio howl is generally caused by some defect in the audio amplifying system.
One of the following defects may be the cause of this howl.
1. Defective Radiotron.
2. Defective "B" battery.
3. Open audio by-pass condensers.
4. Defective grid leak or open grid of any tube in the Radiola.
5. Open R. F. grid resistor.
6. Open by-pass condenser across secondary of first audio transformer.
ACROSS RESISTANCE . R - E OR 1000 VOLTS
TO SE MEASURED I MILLIAMPERES
0-7
6 VOLTS
200 OHMSte
Figure 6-Schematic circuit for resistance measurement
(17) DISTORTED REPRODUCTION
Under normal conditions Radiola 16 will deliver a strong signal of good quality to
the loudspeaker. If the loudspeaker production is poor, test the loudspeaker input from
the receiver. A pair of phones or a loudspeaker of known quality may be used for this
purpose. If the output of the Radiola is of poor quality the distortion may be due to
any of the following causes:
1. Excessive voltage on R. F. amplifiers.
2. Excessive filament voltage.
3. Defective Radiotrons. The Radiola may be operating properly, but a poor tube
in the detector or audio stages will cause distortion.
4. An open audio transformer may cause distortion.
(18) ACOUSTIC HOWL
This is caused by a microphonic Radiotron, or the Loudspeaker being too close to
the Radiola. The sound waves from the loudspeaker striking a Radiotron may cause the
Radiotron elements to vibrate, which in turn, produces an amplified howl in the output of
the loudspeaker.
The remedy lies in interchanging the Radiotrons. Counting from left to right the
third Radiotron is the most susceptible to this microphonic condition. Interchanging it,
with one of the R. F. amplifiers or placing the Loudspeaker at a greater distance from
the receiver will generally remedy this condition, In some cases both may be necessary.
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(19) BATTERY CABLE
Radiola 16 has one battery cable consisting of six conductors and a, separate cord
for the antenna connection (See Figure 1). The color scheme for the connections is
shown on a small card attached to the cable. This color scheme is as follows:
Antenna Blue (Separate from the main cable)
+A 6V Yellow
-A Black with yellow tracer
-B+C Gnd. Green with red and blue tracers
+B 45V Maroon
+B 67V Maroon and Red
+B 135V Red
-C QV Black with green tracer
%" %%".
15J A.F. ,iDETECTOR 3RD R.F. ' 2ND R.F. I sT R.F.
Figure 7-The correct filament polarity of the various Radiotron sockets in
RCA Radiola 16
(20) REFINISHING MARRED SURFACES
The chassis assembly of Radiola 16 is finished in a dark bronze color that gives it a
pleasing appearance and protection against rust or corrosion. When service work is being
performed this surface is likely to become scratched, making a poor appearing job.
The RCA will supply to dealers and distributors through its service stations, small
bottles or cans of refinishing paint, which together with a camel's hair brush should be a
part of the service man's kit when servicing Radiola 16.
This tlronze paint can also be used on the RCA 100A Loudspeaker.
(21) CONTINUITY TESTS
The following tests will show complete continuity for the circuits of Radiola 16.
The volume control should be adjusted so that half its resistance is in the circuit, the
antenna lead disconnected and the battery cable disconnected from all batteries and placed
so that none of its leads will make contact with any other lead. Close operating switch.
A pair of headphones with at least 4/ volts in series or a voltmeter with sufficient
voltage to give a full scale deflection when connected directly across battery terminals
should be used in making this test. This arrangement will be found to be very sensitive
in checking voltage drop in various circuits.
The contacts of the test equipment should be placed across the terminals or leads
indicated in the following test table under the column 'marked "Terminals." If the results
are negative the cause of such negative effect will be found in the last column under the
heading "Incorrect Effect Caused By." The second column indicates the correct effect.
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The designation "P" and "G" refer to the plate and grid contacts of the socket
indicated by the number following. For example G2 would indicate the grid contact of
the second socket, P6 would indicate the plate contact of the sixth tube socket.
Polarity of the various Radiotron sockets are not alike. Figure 7 illustrates the
correct polarity of the filament terminals for each socket in addition to the location of
the plate and grid terminals.
CONTINUITY TEST CHART
Terminals
H-A to +1.1, 2, and 3
+A to +F4, 6 and 6
-A to -F1, 2, 8, 4, 5
and 6
-A to -F6
(Open and close switch
while making test)
-F4 to +F4
-B to +185B
-B to +671/2
-B to frame
-B to GI, G2 or G8
-B to P4
-B to G4
+F4 to +F3
+F6 to +A
+671/2 to Pl
+671/2 to P2
+671/2 to P3
+45 to P4
+185 to P5
+135 to Output
P6 to Output
-9C to G5
-9C to G6
Antenna to frame
G1 to frame
Stator condenser
No. 1 to G2
Stator condenser
No. 2 to G3
Correct Effect
Closed
Closed
Closed
Open or closed ac-
cording to posi-
tion of switch
Closed
Open
Open
Closed
(Switch closed)
Closed
Open
Closed
(very weak)
Closed
Closed
Closed
Closed
Closed
Closed
Closed
Closed
Closed
Closed
Closed
Closed
Closed
Closed
Closed
Incorrect Effect Caused By
Open volume control, filament resistor,
or wiring
Open filament resistor or wiring
Open switch, defective cable or wiring
Defective switch or connections
Open detector grid resistance
Defective 1 mfd. by-pass condenser
Defective 1/2 mfd. by-pass condenser
Open ground connection to chassis
frame
Open secondary of radio-frequency
transformers or grid resistances
Defective A. F. by-pass condenser
Defective grid leak or detector grid
resistance
Open volume control
Open filament resistor
Open primary 1st R. F. Transformer
Open primary 2nd R. F. Transformer
Open primary 3rd R. F. Transformer
Open primary 1st A. F. Transformer
Open primary 2nd A. F. Transformer
Open Connection
Open Connection
Open secondary of first audio trans.
Open secondary of second audio trans.
Open antenna inductance or connections
Open antenna inductance or connections
Open grid resistance No. 1
Open grid resistance No. 2
(22) IMPORTANT PRECAUTIONS
1. As a fixed resistor is used in the filament circuit, it is important that all the
Radiotrons be in place before turning on the operating switch. This is to protect the
Radiotrons from excessive filament voltage when the total load is not in the circuit.
2. The main tuning condensers are electrically and mechanically aligned at the
factory. Tampering with or handling of any kind that may affect the alignment of these
condensers is to be avoided. The screws on the side of the assembly should not be touched
because any movement, even though slight, may seriously affect the overall efficiency of
the Radiola. This would be especially noticeable on weak signals.
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PART II-MAKING REPLACEMENTS
(I) REPLACING ANTENNA COIL
The following procedure should be used when replacing the antenna coil:
(a) Remove five screws holding wooden back panel to cabinet.
(b) Remove knobs on "Station Selector" and "Volume control."
(c) Unscrew threaded round collar from front of battery switch.
(d) Remove four screws holding chassis in place to bottom of cabinet.
Figure 8-Removing chassis assembly from cabinet
The chassis assembly may now be removed by slightly rocking it in the cabinet and
slipping it out of the rear opening. See Figure 8. This brings the complete chassis into
view, allowing an easy examination of all parts.
The antenna coil is located at the left end viewed from the rear of the cabinet-the
end that has the condenser drum and scale. See Figure 9. To remove the coil unsolder
the two leads and remove screw and nut that passes through center of coil. The new
coil is then placed in the position occupied by the old one. The nut and screw are replaced
and the Radiola is reassembled in the reverse of the foregoing order. Before being replaced
in the cabinet it should be given an operating test.
(2) REPLACING RADIO FREQUENCY COILS
The three radio frequency transformers together with a mounting strip and two
pin jacks are stocked as one complete unit.
A step by step procedure for replacing this assembly is as follows:
1. Remove chassis from cabinet as described in Part II, Section 1.
2. Unsolder and carefully tag all connections to the three transformers and the
two pin jacks.
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3. Remove four screws that hold mounting strip to metal chassis. The entire
assembly can now be released. The new assembly should be placed in the
same position occupied by the one just removed.
4. Replace the four screws that hold mounting strip to metal chassis.
5. Replace and resolder all leads to the three transformers and two pin jacks as
indicated by the tags previously attached to them.
ANTENNA lsr R.F. 2*R. F.
COIL TRANSFORMER TRANSFORMER 3"D R FILAMENT
TRANSFORMER RESISTOR
GRID COND.
-GRID LEAK
A.E
CONDENSER
2"°R.FGRID 3"°R.FGRID BY-PASS A.F VOLUME
RESISTOR RESISTOR CONDENSERS TRANSFORMERS CONTROL
Figure 9-Sub-chassis assembly showing antenna coil, radio frequency coils, by-pass
condensers, resistances and audio frequency transformers
6. Give Radiola an operating test before replacing in cabinet to determine that
replacement has been properly made.
7. Return chassis assembly to cabinet and replace all screws and control knobs.
(3) REPLACING GANG SOCKETS
The sockets of Radiola 16 are of the gang variety, using one detector socket, a two-
gang A. F. socket strip, and one three-gang socket strip for the radio frequency amplifier
tubes.These sockets are riveted to the metal chassis. To replace these sockets drill out
the old rivets and use screws, nuts and lock washers for securing the new sockets. A step
by step procedure for making replacements of this kind is as follows:
1. Remove chassis assembly from cabinet as described in Part II, Sec. 1.
2. Remove and tag all leads to the terminals of the sockets being removed.
3. Drill out rivets holding sockets to metal chassis frame.
4. The socket assembly may now be removed and the new one placed in the position
occupied by the old one.
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5. Fasten new socket in place by using small round head machine screws, nuts and
lock washers in place of the rivets previously drilled out.
6. Resolder all connections to terminals of new sockets.
7. Test Radiola and replace in cabinet.
(4) REPLACING MAIN TUNING CONDENSERS AND DRIVE
The main tuning condensers are replaced as one complete unit. A step by step
procedure is as follows:
1. Remove chassis assembly from housing as described in Part II, Sec. 1.
2. Unsolder four connections to condenser.
3. Remove three screws from under side of chassis that holds condenser assembly.
4. The assembly may now be removed and the new assembly placed in position.
5. Replace three screws that hold assembly in place and resolder the four leads.
6. Replace chassis assembly in cabinet.
TO PLATE YELLOW-
Is? A.F.
BLACK WITH.-
GREEN TRACER'
CABLE -I
TO GRID
2"-° A.F.
TO JACK GREEN
A. F. CONDENSER 1.001 MFD.
TO PLATE
(YELLOW DETECTOR.
--BLUE
TO GRID
ISY A. F.
TO MAROON
GREEN ON CABLE
Figure 10-Audio frequency transformers and color scheme of connections
(5) REPLACING LARGE BY-PASS CONDENSERS
These condensers, located on the under side of the chassis frame, are held together
by means of clamps that form part of the condenser case fastened to the frame. A step
by step procedure when making replacement is as follows:
1. Remove chassis from cabinet as described in Part II, Sec. 1.
2. Remove condenser assembly as described in Part II, Sec. 4.
3. The tabs of the condensers may now be bent up, by using a screw driver.
4. The-two condensers are released as a unit from the chassis frame. Separate
them by turning up the tab that holds them together.
5. Unsolder the leads of the condenser that is to be replaced. Insert the new
condenser in the place occupied by the old one and resolder the leads to it.
6. Fasten the condensers together as a unit by binding over the tabs provided for
that purpose. Fasten to frame by inserting the tabs of the condenser into their
respective slots and bending the tabs over on the top side of the frame.
7. Replace condenser assembly as described in Part II, Section 4, and then replace
chassis assembly in cabinet as described in Part II, Section 1.
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(6) REPLACING AUDIO TRANSFORMERS
The audio transformers of Radiola 16 are built together as a unit.
replacement the following procedure should be used.
1. Remove chassis from cabinet as described in Part II, Section 1.
2. The audio transformer case is held by metal tabs, bent over on the
the chassis. Turn these up to release the transformer assembly.
3. Tag and unsolder all leads.
4. Place the new transformer assembly in position occupied by the old
frame by bending over metal tabs that hold it in place.
5. Solder all leads in place as indicated by tags attached. The col
these connections is shown in Figure 10.
6. Replace chassis assembly in cabinet.
(7) REPLACING CONDENSER DRIVE CABLE
In making a
upper side of
and fasten to
or scheme of
The condenser drive cable of Radiola 16 is made of phosphor bronze and is very
rugged. If replacement becomes necessary the following procedure should be used.
1. Remove chassis from cabinet as described in Part II, Section 1. Place chassis
on table in normal position with controls to the front.
2. Release the cable adjusting screw and clamp, and remove old cable from large
drum and grooved drums completely.
3. Starting from the rear grooved drum place eye of cable over pin, wind on three
complete turns, and then bring cable up to large drum. I'he pin in the grooved
drum should be nearly horizontal and on the right side of the drum.
4. Now bring cable over the large drum. Turn drum so that cable adjusting
screw is on top. Pass cable over groove until point is reached where there is a
slot in the drum for passing cable to the other side of drum to the other track.
5. Follow on.around other track in same direction until point is reached where
cable is directly above front grooved drum.
6. Starting on the third groove back from the front of the grooved drum wind on
two and a half turns and slip eye over pin.
The cable is now in the correct position, although probably slack.
The cable adjusting screw and clamp that were previously removed to allow the
cable to pass along the groove are replaced. By slipping the clamp over the cable and
gradually turning up on the cable adjusting screw, the cable may be tightened until
there is no last motion in any of the controls. Care should be taken not to take up too
much as the cable may be stretched or possibly broken.
(8) REPLACING DIAL SCALE
After considerable use a dial scale may become dirty or illegible and a new scale
desired. A step by step procedure of making replacement follows:
1. Open lid of cabinet of Radiola.
2. Turn dial so that the two screws that hold the dial in place are on top.
3. Remove screws, washer and nuts that hold dial in place.
4. Replace old dial with new one and replace screws, but do not tighten.
5. Examine new dial from front of Radiola to see that numbers on dial are not
upside down and the maximum and minimum figures are in their correct places.
6. Tighten screws holding dial in place and close lid of cabinet.
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Before
poor quality,
defective batteries,
tion is not due
detailed causes.
SERVICE DATA CHART
Chart, when experiencing no signals, weak signals,
howling and fading, first look for defective tubes.
and a poor antenna system. If imperfect opera-
Data Chart" should be consulted for further
using the following Service Data
noisy or intermittent reception,
wrong battery connections
to the above causes the "Service
Indication Cause Remedy SEE SERVICE NOTER
Part 1 Part 11
oNoSignals-
Defective operating switch . .
Loose volume control arm . .
Defective battery cable . . .
Defective antenna coil . . .
Defective R. F. transformer .
Defective A. F. transformer .
Defective By-pass condenser .
Replace switch
Tighten volume control arm
Replace battery cable . .
Replace antenna coil . . .
Replace R. F. transformer as-
sembly
Replace A. F. transformer as-
sembly
Replace By-pass condenser .
-Sec. 9
Sec. 19
---
---Sec. 1
Sec. 2
Sec. 6
Sec. 5
Weak
Signals
Defective cable
Defective antenna coil .
Defective R. F. transformer .
Defective A. F. transformer .
Dirty prongs of Radiotrons . .
Defective By-pass condenser .
Defective main tuning condenser
Replace cable
Replace antenna coil . .
Replace R. F. transformer as-
sembly
Replace A. F. transformer as-
sembly -
Clean Radiotron prongs . .
Replace defective By-pass con-
densers
Replace main tuning condenser
assembly
Sec 19
---Sec. 8
--
-Sec. 1
Sec. 2
Sec. 6
-Sec. 5
Sec. 4
Poor
Quality
High plate voltage on R. F
amplifiers
Defective A. F. transformer
Defective By-pass condenser .
Reduce plate voltage to 67 on
R. F. amplifiers . . . ..
Replace A. F. transformer as-
sembly
Replace defective condenser .
Sec. 13
-- -Sec. 6
Sec. 5
Noisy or
Intermit-
tentReception
Dirty Radiotron prongs .
Loose volume control arm .
Socket contacts bent or broken .
Clean Radiotron prongs with
fine sand paper . . . .
Tighten volume control arm . .
Repair or replace defective con-
tact
Sec. 8
Sec. 9
Sec. 7
---
Howling
High plate voltage on R. F
amplifiers
Open grid resistors . . .
Defect in audio system . .
Acoustic howl caused by micro-
phonic Radiotrons or loud-
speaker too close to Radiola .
Open grid circuit in any stage .
Reduce plate voltage on R. F.
amplifiers to 67 . . .
Check and replace grid resistors
Check and repair defect in audio
system
Interchange Radiotrons or in-
crease distance of loudspeak-
er from Radiola . .
Check circuits and repair defect
Sec. 13
Sec. 21
Sec. 16
Sec. 18
Sec. 21
---
- --
Radiotrons
fail to
light
Operating switch not "On" . .
Defective operating switch .
Defective volume control .
Defective cable . . . .
Turn switch "On" . . .
Replace operating switch
Correct defect or replace vol-
ume control, . . . . .
Repair or replace cable . .
--Sec. 9
Sec. 19
-----
Play in
station
selector
Loose knob
Slack cable Tighten or replace knob . .
Take up on cable at adjusting
screw
Sec. 11
Sec. 10
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