Radio Corporation Of America 100 Operating and maintenance manual

RCA LOUDSPEAKER
MODEL 10 0
Reg. U. S. Pat. Office
SERVICE NOTES
NS-100-2
Second Edition-November, 1926
RADIO CORPORATION OF AMERICA
326 Broadway
New York City
Prepared by
NATIONAL SERVICE DIVISION
233 Broadway, New York City
DISTRICT SERVICE STATIONS
10 South La Salle Street
Chicago, Ill.
3308 Fourteenth Street, N. W.
Washington. D. C.
28 Geary Street
San Francisco, Cal.
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A Word or Two About Service
Service goes hand in hand with sales. The well informed Radiola 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 National Service Division
of the RCA has prepared a series eef 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 Radiola Dealers' service prob-
lems, 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 valu-
able 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 1926-Radio Corporation of America
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RCA Loudspeaker Model 100 Service Notes
Non.-Cone assembly of RCA Loudspeaker Model 102 is
identical to Model .100 less the filter unit
Prepared by
NATIONAL SERVICE DIVISION
Instructions NS-100.2
PART I
RCA Loudspeaker Model 100 is of the free floating cone type. It is suspended at
the outer edge'by means of a strip of soft kid which holds the cone in a central position
but does not impede its movement to any great degree. The cone is attached rigidly to
the speaker mechanism at the center.
In servicing Model 100 Loudspeaker always make certain that the output of the
Radio Receiver used in conjunction with it, is of good quality. If distortion is present in
the Radio Receiver, RCA Model 100 Loudspeaker will reproduce that distortion as
faithfully as it does the tone variations of the program.
Rattling sounds, or the so-called "paper rattles," are generally caused by a distor-
tion in the lower tone registers of the amplifying system of the Radio Receiver. It is
therefore quite important to first check the Receiver for quality of signal. This may
be done by substituting another loudspeaker of known quality or else by replacing the
loudspeaker with a pair of headphones. If distortion is present either in the second
loudspeaker or the headphones it is a positive indication that the trouble is originat-
ing in the Radio Receiver.
Similarly, if the Radiotrons in the Receiver are overloaded by an abnormally strong
signal being forced through the amplifiers, distortion will follow.
If it is definitely established, however, that the distortion or rattle complained of is
not due to a defect or improper adjustment of the Radio Receiver, but is apparently
caused by the Loudspeaker itself, it may be the result of one of the following conditions:
(A) Foreign material interfering with armature vibration.
(B) Armature striking the pole piece.
(C) Cone misaligned.
(D) Excessive pressure on the stylus.
(E) Bent stylus.
(F) Loose or bent connecting rod.
Figure 1 shows a rough sketch of the complete armature assembly and its relation
to the cone. The armature vibrates between the pole pieces (not shown), this motion
being transmitted through the stylus to the thrust lever. The thrust lever is held rigidly
to one of the motor side pieces. It is attached rigidly to the cone by the connecting rod.
Dirt at any of these points may cause distortion.
On inspecting the RCA Model 100 Loudspeaker, note whether or not the stylus is
bent, if so straighten it. The cone is attached to the connecting rod by means of a small
nut "B", Figure 1. The end of the connecting rod is threaded. Make certain that the
cone is drawn up tight to the connecting rod.
If the two foregoing points have been checked and found to be O.K., note whether or
not the armature is striking the pole pieces. Figure la and Figure 2 show the relation
of the armature to the pole pieces. There should be a space approximately .010 inch
Between the armature and the pole pieces, Figure la. This is true at both ends of the
armature. 3
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Fig. 1-Moving part of motor
Fig. la-End view of motor
Method of adjusting armature clearance
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If either end of the armature strikes the pole piece a very disagreeable rattle will
result. To correct a misalignment of the armature a pair of spacer tools, shown in
Figure 3, and a screwdriver will be necessary. These spacer tools should be made
of .010 phosphor bronze stock aborit 1/8 inch wide. The distance between the open
ends of the tool should he .091 inches. See Figure 3a.
Any loose screws, nuts or parts in the speaker may cause rattles and for that reason
in making adjustments all screws should be seated properly, which means that all screws
and nuts should be drawn up firmly enough to prevent their loosening when the speaker is
placed in operation. Care should be taken to prevent stripping of the threads on the
screws and nuts as well as to prevent torsion of the elements held in place by such
screws and nuts.
To readjust the armature it will be first necessary to free it. Figures 4 and 5 show
the method of doing this. The screws shown as "C" should be backed off about two
turns. Do not remove them entirely.
When the two screws are loosened it is a simple matter to insert one of the spacer
tools between each of the two armature ends and the pole pieces as shown in Figures 6
and 7.When the spacing tools are inserted the clearance between the armature and the
pole pieces must necessarily be the required ten thousandths as this is the thickness
of the blades of the two spacers.
After the spacer tools have been inserted, one at each end, the two screws "C" that
were loosened (Figures 4 and 5) should be tightened firmly. Figure 8 shows the method
of tightening the upper screw with the spacers in place.
After the two screws have been tightened the spacer tools should be removed
and the Loudspeaker tested. If the rattle has been eliminated no further adjustment will
be necessary. If, however, the rattle is still present it may be due to the fact that the cone
is out of centre with respect to the connecting rod.
To correct this, again refer to Figure 2. The screw "d" holds the thrust lever.
When this screw is loosened the cone will automatically assume the proper position and
the screw "d" should then be tightened down. Care should be taken that the sides of the
thrust lever, visible in Figure 2, be held at right angles to the pole pieces as shown when
tightening "d".
The Loudspeaker should again be tested. If the rattle still persists it is probably due
to an excessive pressure on the connecting rod which may be corrected as shown in Figure
9. A soldering iron should be applied to the point where the inner end of the stylus is
soldered to the thrust lever. The solder at that point should be softened sufficiently to
allow free movement of the stylus. Here again the adjustment is automatic and it is only
necessary to keep the solder soft until this readjustment takes place.
PART II
Should it become necessary to replace the field coils due to burn-out or other causes,
it will be necessary to remove the entire reproducer unit.
The procedure is as follows:
1. Remove the flexible leads of the coils from the binding posts. Tag the leads
as they are removed so that when the unit is reassembled they may be connected to the
proper binding posts. THIS IS IMPORTANT.
2. Remove the small nut holding the cone to the connecting rod shown in Figure 1.
5
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3. Remove the nuts F, Figure 10, from the upper supporting screws "H". A
small open end wrench will be necessary for this operation as it is necessary to remove
these nuts by inserting the wrench between the cone and the frame.
4. Unscrew the lower supporting screw G, Figure 9, and remove the strap "N".
5. Remove the unit by pulling out. Do not strain the cone or the connecting rod
when removing the unit. Make certain that the connecting rod slides out freely as the
unit is removed.
6. Remove the two screws "H", Figure 10, holding the motor in place. These
screws thread into the spacer bushings "E".
7. Place a piece of iron on the ends of the horseshoe magnet and slide the motor
off. The piece of iron takes the place of the motor and acts as a keeper on the magnet.
8. Remove the screw holding the thrust lever to the motor frame "D", Figure 2.
9. Unsolder the thrust lever from the stylus and remove Point "E", Figure 1.
10. Remove the two armature screws "C", Figures 4 and 5.
11. Dissemble the motor by removing the two countersunk screws. One of these
screws "K" is shown in Figure 2. The coils are then accessible, but the armature is still
in position in the center of the coils. Figure 11.
Fig. 3-Spacer tools
.091.
.010 0.125« {-
Fig. 3a-Spacer tool dimensions
Freeing the armature
6
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12. Slip one coil over the free end of the armature and then slip the second coil
off the armature and stylus. All parts before re-assembling should be thoroughly
cleaned and freed from all traces of dust or dirt and metal filings, etc. Use a brush to
remove foreign matter from the parts. Avoid the use of liquid cleaners as they often
induce corrosion.
The re-assembly should be a reversal of the operation just described.
1. Place the coils "P"-"P", Figure 11, in proper position around the armature.
The small length of wire connecting the two coils in series should be at the outside of
each coil when assembled, "L", Figure 11.
2. Place the coils with armature in position onone of the motor side pieces, Figure
12. Place the other motor side pieces in place and screw the assembly together by means
of the screw. In making this assembly make certain that the small pins "M", Figure 12,
projecting from the inner side of the motor side piece, separate the two field coils as shown
in "B", Figure 12.
3. Place the thrust lever in position and screw it in place "d", Figure 2, but, do
not solder to the stylus at this time.
4. Replace the armature screws "C", Figures 4 and 5, but do not seat them firmly.
5. Insert the spacer tools (Figure 3) in position at the top and bottom of the
armature and tighten down the armature screws as described for adjusting the armature
in Part I of these instructions.
6. It will sometimes happen that in tightening the armature screws the armature
may be strained slightly and when the spacer tools are removed the strain causes the
armature to spring out of the central position. Remove the spacer tools and note care-
fully whether or not the armature is centered between the pole pieces. If not repeat
operation No. 5.
7. Remove the keeper and place the motor in position on the horseshoe magnet.
Before seating the screws "H", Figure 10, that hold the motor to the magnet push both
sides of the motor down toward the curved part of the magnet. The motor should be
horizontal with respect to the sides of the magnet.
8. Replace these assembled units on the Loudspeaker frames. Place the connecting
rod through the cone. Place the lower supporting strap "N", Figure 9, in place and
tighten screw "G" until the unit is held in position, but not firmly.
9. Adjust the position of the unit until the connecting rod in passing through the
center of the cone does not exert a vertical or horizontal pressure on the cone.
10. Seat the screw "G" holding the lower strap "N", Figure 9, and then fasten
the upper portion of the unit to the frame by means of the nuts "FF", Figure 10, on the
upper screws "HH". When tightening these last two mentioned nuts be careful not to
disturb the central position of the unit as established in 9.
11. Lock the cone to the connecting rod by the nut provided for that purpose.
The thread on this nut has a pitch of 80 threads to the inch and it may be stripped
very easily if too great a pressure is applied to it.
12. Solder the stylus to the thrust lever (Figure 1).
13. Reconnect the leads to the binding post.
14. Test the loudspeaker and if further adjustments are necessary follow the pro-
cedure outlined in Part I of these instructions.
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Fig. 6-Spacer tool in place. upper armature end Fig. 7-Spacer tool in place, lower armature end
Tightening upper armature holding screw
PART III
Soldering the stylus to the thrust lever
'l'o replace a defective cone:
1. Remove the small nut that holds the cone to the connecting rod.
2. Remove the four screws "a", "b", "c and "d" shown in Figure 13. When these
screws are removed the entire aluminum frame may be removed from the casing. If
desirable, the leads may be disconnected, but this is not necessary.
3. Remove the remaining eight screws shown in Figure 13 as
"k" and "1".
J
4. Remove the outer clamping ring.
5. Remove the cone.
8
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6. Put new cone in place. Make certain that the connecting rod passes through
the center hole in the aluminum cone cap.
7. Place. the cone and outside clamping ring so that all screw holes correspond
with the screw holes in the casing.
8. Replace the screws, "e", "f", "g", "h", "i", "j", "k" and "1" (Figure 13). These
screws should be tightened down uniformly. Do not seat one screw at a time, but tighten
each little by little until all are seated properly.
9. Provide supports and lay the casing on them in a horizontal position.
10. Allow the aluminum frame to rest on the four cleats "O", Figure 13, on the
front edge of the casing.
11. Center the frame in the center of the casing and replace the four screws "a",
"b", "c", "d", Figure 13.
12. Test the speaker and make final adjustments.
While making these adjustments the loudspeaker should be kept in a clean place
free from dirt or filings. Small particles of metal are easily attracted to the mechanism
in the loudspeaker due to its magnetic qualities.
Motor and connection to cone
Motor side piece showing separator pins
9
Coils in place around armature
Frame, front view
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Fig. 14
Cylindrical filter type
lo
Fig. 15
Square filter type
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