RCA Radiola 17 Service Notes
RCA
Radiola 17
SERVICE NOTES
RCA Radiola 17
First Edition—Nov. 1927 R17—1
Radio Corporation of America
SERVICE DIVISION OF THE PRODUCTION AND SERVICE DEPARTMENT
233 BROADWAY, NEW YORK CITY
DISTRICT SERVICE STATIONS
326 Broadway 1412 Monroe St., N. W. 2001 West Pershing Road 274 Brannan St.
New York City Washington, D. C. Chicago, 111. San Francisco, Cal.
A WORD OR TWO ABOUT SERVICE
Service goes hand in hand with sales. The well informed RCA Dealer renders service at time of
sale in affording information as to proper installation and upkeep. Subsequent service and repair may
be required by reason of wear and tear and mishandling, to the end that Radiola owners may be
entirely satisfied.
Obviously this service can best be rendered at point of contact and therefore Dealers and
Distributors who are properly equipped with a knowledge of the design and operation of Radiolas
occupy a favorable position to contract for this work.
To assist in promoting this phase of the Dealers' business the Service Division of the RCA has
prepared a series of Service Notes—of which this booklet is a part—containing technical information
and practical helps in servicing Radiolas.
This information has been compiled from experience with RCA Dealers' service problems, and
presents the best practice in dealing with them. A careful reading of these Service Notes will establish
their value to Dealer and Distributor, and it is suggested they be preserved for ready reference.
In addition to supplying the Service Notes the RCA, through its Service Stations, has available
to Dealer and Distributor the services of engineers who are qualified to render valuable help in solving
service problems.
Property of Radio Corporation of America. Confidential and to be used only by its authorized distributors
and dealers in furnishing service in connection with its apparatus.
Copyright 1927—Radio Corporation of America.
Page
2
5
32
Page
Radiotron Sequence .................................................... 6
Circuit Characteristics ................................................ 6
Radiotrons.....;..................................................... 7
Antenna Installation (Outdoor)........................ 8
Antenna Installation (Indoor)........................... 9
Ground ........................................;.............................. 9
Antenna System Failures ....................................... 10
Radiotron Sockets...............:.............................. 10
Radiotron Prongs........................................................ 10
Loose Volume Control Contact Arm.......... 11
Adjustment for Slack Drum Control........ 11
Mechanical Hum......................................................... 12
Broken Condenser Drive Cable........................ 13
Loudspeaker Polarity .
Uncontrolled Oscillation
Distorted Reproduction
Audio Howl ......................
Acoustic Howl ........
Hum ............................
Line Control Switch ............
Wiring Cable .............................
Pilot Lamp and Canopy
Filter Condensers ..................
Voltage Readings ..................
Grid and Plate Voltages
Heating of Cabinet ...............
Continuity Tests .....................
Page
13
. 14
.... 15
.. I5
.... 16
... .16
......18
..... 19
..... 19
..... 20
..... 20
..... 21
..... 22
..... 23
Page
Replacing Volume Control ........................................... 24
Replacing Radio Frequency Coils................................... 25
Replacing Radiotron Gang Sockets................................. 26
Replacing Main Tuning Condensers and Drive …...... . 26
Replacing Large By-Pass Condensers............................. 27
Replacing Audio Transformers ....................................... 28
Replacing Output Transformer........................................ 28
Page
28
29
30
30
31
31
31
Replacing Condenser Drive Cable.........
Replacing Dial Scales............................................
Replacing Power Cable................................
Replacing Filter Condenser Assembly....
Replacing Either Power Transformer or Filter Reactor
Replacing Terminal Strip
Replacing Miscellaneous Parts in S.P.U....
R F. Transformer Connections...................................24
By-Pass Condenser Connections................................25
A. P. Transformer Connections..................................26
Output Transformer Connections...............................26
Replacing Dial Scales ...............................................27
Color Scheme of Power Cable Connections………. 29
A Word or Two About Service ………
Introduction …………..........................
Service Data Chart................................
CONTENTS
PART I—SERVICE DATA
PART II—MAKING REPLACEMENTS
RCA Radiola 17 ...............„.............................:........ 1
Top View of Chassis Assembly................................. 4
Socket Power Unit Showing Parts.................................. 5
Radiotron Sequence ................................................... 5
Schematic Circuit Diagram of Receiver………………. 6
Schematic Circuit Diagram of S.P.U.............................. 7
Radiotron Socket Contacts ........................................ 8
Method of Cleaning Radiotron Prongs.......................... 9
Releasing Volume Control ......................................... 10
Adjusting Contact Arm of Volume Control ................ 11
Turning Cable Adjusting Screw...... …………… .. 12
Condenser Cable and Drum Mechanism……………. 13
Schematic Circuit for Resistance Measurement.......... 14
Adjusting Potentiometer tor Minimum Hum ............. 16
emoving Receiver Assembly from Cab-22
ILLUSTRATIONS
Page
View of Pilot Light Socket and Canopy. …….….... 17
Wiring Diagram of Sub-Chassis Assembly ……....... 18
Continuity Wiring Diagram of S.P.U.......................... 19
Internal Connections of Filter Condensers ............... 20
Schematic Circuit for Securing Grid Voltages.......... 21
Removing Receiver Assembly from Cabinet…… ….22
Page
ANTENNA AND
GROUND
CONNECTIONS
POWER CABLE TUNING CONDENSERS OUTPUT TRANSFORMER
Figure 1—Top view of chassis assembly showing the principal parts.
TERMINAL
STRIP
RCA RADIOLA 17
SERVICE NOTES PREPARED BY RCA SERVICE
DIVISION
INTRODUCTION
RCA Radiola 17 is a six-tube tuned radio frequency receiver (Figure 1), utilizing RCA Radiotrons
UX-226, UY-227, UX-171 and the Radiotron full wave rectifier UX-280 in the socket power unit
(Figure 2). The use of Radiotrons UX-226, UY-227, and UX-171, using raw alternating current for
filament supply,
FILTER CONDENSERS FILTER REACTOR POWER TRANSFORMER
Figure 2—Socket Power Unit showing various parts.
and Radiotron UX-280 in a plate and grid supply unit makes Radiola 17 a complete socket power
receiver operating on 105-125 volts, 50 to 60 cycle A. C. lines.
Very little service work should be required on Radiola 17. However, the following notes are
published for the guidance of those called upon to locate and remedy any trouble that may occur.
To
Ant
6 5 4 3 2 1
nd
2
1st Detector 3rd 2nd 1
A.F. A.F.
R.F. R.F. R.F.
st
Radio Frequency
To
Loudspeaker
Figure 3— Radiola sequence in RCA Radiola 17
PART I—SERVICE DATA
(1) RADIOTRON SEQUENCE
Figure 3 illustrates the sequence of the Radiotrons in the receiver proper, omitting Radiotron UX280 in the socket power unit. 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.
Radiotron No. 2 is a stage of tuned R. F. amplification employing a grid resistance to prevent
oscillation. It is tuned by the first gang condenser.
Radiotron No. 3 is the second stage of tuned E. F. amplification. It also
Figure 4—Schematic circuit diagram of receiver assembly.
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 detector tuned by the thirdgang condenser. 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 UX-171.
(2) CIRCUIT CHARACTERISTICS
The following principles are incorporated in the circuit design of Radiola 17
(Figure 4 and 4A.)
1. A three-gang condenser, employed to tune two of the radio frequency circuits and the detector
circuit, provides one tuning control.
2. An aperiodic antenna, or first E. F. circuit, eliminates the necessity for a separate antenna tuning
control.
3. The volume control regulates the input grid voltage to the first R. F. amplifier stage. This is the most
practical method of volume control for use
6
with A. C. Radiotrons and gives a smooth control of volume without distortion.
4. No neutralizing condensers are employed. Grid resistances in the two tuned radio frequency stages
effectively prevent any tendency to self oscillation.
5. Raw A. C. of the correct voltage is used for filament heating of all Radiotrons. This eliminates the
use of "A" batteries.
6. The three B. F. stages and the first audio stage receive a plate voltage of 135 volts in conjunction
with a negative grid bias of 9 volts. The detector receives 45 volts plate supply without grid bias. The last
audio stage receives a, plate supply sufficient to provide ample loudspeaker output. The plate and grid
voltages are supplied by means of a built-in " B " and " C " supply using Radiotron UX-280 as the
rectifying device.
7. Radiotron UX-171 in the last audio stage provides ample volume without distortion in loudspeaker
reproduction.
Figure 4A—Schematic circuit diagram of socket power unit.
The various circuit characteristics of Radiola 17 provide for easy installation and simple operation
coupled with quality reproduction delivered to the loudspeaker.
(3) RADIOTRONS
Radiotrons UX-226 are used in all radio frequency amplifying stages and in the first audio
amplifying stage. It has an oxide coated filament consuming 1.05 amperes at 1.5 volts.
Radiotron TJY-227 is used for the detector. It operates on raw A. C. for filament supply, making
use of an indirectly heated cathode. This Radiotron has five prongs, the extra prong being connected to
the oxide coated cathode. Under normal conditions Radiotron UY-227 should give little trouble.
However, in some cases a slight howl may develop in the detector circuit which will necessitate
substituting another UY-227 Radiotron. Although a howl may develop in a receiver with one UY-227,
in another the same tube may prove 0. K. On examining a Radiotron UY-227 in operation, a slight
flickering of the heater
7
(4)
element, incased in its insulating material, may be noticed. This condition in no way affects the normal
operation of the Radiotron. The lag in the transference of heat from the heater element to the cathode, as
evidenced when starting and stopping the operation of the tube, takes care of any variations indicated by
this flicker, which supposedly might affect the normal operation of Radiotron UY-227. In Radiola 17
there is a positive potential of 9 volts applied to the cathode of Radiotron "UY-227 with the negative side
of this potential connected to the center connection of the potentiometer across the heater winding for this
Radiotron. This prevents a possibility of the cathode emitting any electrons back to the heater instead of
to the plate.
The power-amplifier Radiotron UX-171 in the last audio stage is interchangeable with the new
EGA Radiotron UX-171A. An output transformer protects the loudspeaker windings from the high plate
voltage used with this Radiotron.
Radiotron UX-280 is a full wave rectifying Radiotron used to rectify the alternating current into
pulsating direct current, which is smoothed out by means of a filtering system, and used to provide all
plate and biasing voltages.
Figure 5—Radiotron socket contacts
ANTENNA INSTALLATION (Outdoor Type)
Due to the high sensitivity of Radiola 17 the most efficient antenna system is one of
approximately 25 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 continuation
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 oxidization effects of the atmosphere.
The antenna and lead-in should be supported by high grade glass or porcelain insulators. 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
use of a flat "window-strip" type of lead-in is not recommended.
8
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 arrester, in accordance with the requirements of the National Fire
Underwriters' Code.
(5) ANTENNA INSTALLATION (Indoor Type)
"Where the installation of an outdoor antenna is not practical, satisfactory results may generally
be obtained by using an indoor antenna consisting of about 25 feet of insulated wire strung around the
picture molding or placed under a rug. In buildings where metal lathing is employed satisfactory
results are not always possible with this type of antenna. Under such conditions 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.
Figure 6—Method used to clean Radiotron prongs.
(6) 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. G-as 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 ground depends upon the moisture present in the soil. The ground lead
should be. connected 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 17 is capable of receiving over good distances when connected to an
efficient antenna and a low resistance ground.
9
If the results of experiments seem to indicate that a good ground 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.
(7) 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 service man should give his first attention. A grating noise may be caused by a poor
lead-in connection to the antenna, or antenna touching some metallic surface, such as the edge of tin
roof, drain pipe, etc. By disconnecting the antenna and ground
Figure 7—Releasing mounting screws holding volume control.
leads from Radiola 17 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.
(8) RADIOTRON SOCKETS
The sockets in Radiola 17 are of the standard gang UX and UY type (Figure 5). The three-gang
socket is for the radio frequency amplifiers; the single socket—a five-prong detector socket is for
Radiotron UY-227 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.
(9) RADIOTRON PRONGS
Dirty Radiotron prongs may cause noisy operation or change the resistance of the filament circuit
sufficiently to cause a hum in the loudspeaker. They should therefore be cleaned periodically to insure
good contact.
10
Loading...