Radio Corporation Of America Radiola 25 User manual

Radiola 25
Super-Heterodyne

Radiola 25
REG. U.S. PAT. OFF
Super-Heterodyne

Instructions 86982
Edition F
Radio Corporation of America
233 Broadway
New York City
10 South La Salle Street 28 Geary Street
Chicago, 111. San Francisco. Cat|

Radiola 25
REG. U.S. PAT. Off.
Super-Heterodyne
INTRODUCTION
RADIOLA 25 is a radio broadcast receiving instrument, utilizing the
super-heterodyne principle, which provides unusual simplicity of
operation, selectivity and sensitivity. The cabinet contains the operating
mechanism and battery equipment, as well as a socket for the loop
antenna which is plugged in through a hole in the top cover, making the
receiver self-contained, with the exception of the Loudspeaker. The
receiver is designed for reception over the broadcast frequency band,
550 to 1360 kilocycles (approximately 550 to 220 meters).
GENERAL
Radiola 25 Super-Heterodyne "A," "B" and "C" supply may be
obtained as described in any one of the following combinations:
1. Complete dry battery operation, in which the "A," "B" and "C"
supply is obtained from dry batteries. This is the form in which
Radiola 25 is normally supplied.
2. "B”voltage may be obtained from either the RCA Duo-Rectron,
Model AP-937, or Radiola Loudspeaker, Model 104, the "A"
and "C" supply being obtained from the usual dry batteries.
(a) R.C.A. Duo-Rectron, Model AP-937 is operated from an al-
ternating-current circuit rated at 105 to 120 volts, 40 to 60
cycles.
(b) Radiola Loudspeaker Model 104 may be operated from an
alternating-current circuit rated at 105 to 120 volts, either
40 to 45 cycles or 50 to 60 cycles.
3. "A," "B" and "C" supply may be obtained from Radiola
Loudspeaker Model 104 (making Radiola 25 entirely operated
from alternating current), by changing Radiola 25 so as to
employ the accessories furnished in the AC Package, Model
UP-971.
3

This booklet describes the operation of Radiola 25 for
dry battery operation only. Instructions describing the use of
the other apparatus referred to will be found accompanying
that apparatus.
The information herein is illustrated to show each step in
the installation of Radiola 25. Read the instructions first, then
follow the pictures, with accompanying descriptions, when
making the installation.
EQUIPMENT REQUIRED
For Dry Battery Operation
The complete installation of the Radiola 25 for dry
battery operation requires the following apparatus:
5 Radiotrons, Model UX-199 (furnished with the
receiver). 1 Radiotron, Model UX-120 (furnished
with the receiver). 1 Loudspeaker, such as
Radiola 100, with Telephone Plug. 1 Set of "A,"
"B" and "C"' batteries, as listed on page 5.
4

BATTERIES REQUIRED
The following batteries are required for complete dry
battery operation.
NOTE.—The fact that the Radio Corporation of America does not list
batteries of all manufacturers is not intended as a reflection on the
products of any battery manufacturer not listed. Any battery having
dimensions, ratings, and satisfactory terminal connections, similar to
those of the batteries listed below, may be used.
(A)—Six standard dry cells, 1½ volts each, such as those listed below,
for lighting the filaments. Approximate size, 21/2 in. by 61/2 in.,
such as:
6 Burgess No. 6 dry cells, or
6 Eveready Dry Cell Radio "A" batteries No. 7111,
or 6 Eveready Columbia Ignitor No. 6 dry cells, or 6
Ray-0-Vac No. 1211 dry cells or equivalent.
(B-1)—Two 22 ½ volt plate batteries, preferably of the VERTICAL
TYPE (connected in series by the connections in the set), such as
those listed below. Approximate size, 4 ¼ in by 3 1/8 in. by 7 1/8
in., such as:
2 Burgess No. 2158 plate batteries,
or 2 Eveready No. 779 batteries, or
2 Ray-0-Vac No. 2153 plate
batteries, or equivalent.
Those of the horizontal type may be used if the vertical type is
not available. Approximate size, 6 3/4 in. by 41/8 in. by 3
1/8 in., such as:
2 Burgess No. 2156 plate batteries, or
2 Eveready No. 766 plate batteries (with cardboard
container) or 2 Ray-0-Vac No. 2151 plate batteries, or
equivalent.
(B-2)—Two 45-volt (extra large) plate batteries (connected in series
by the connections in the set). Approximate size, 8 3/16 in. by 4
7/16 in. by 7 3/16 in., such as:
2 Burgess No. 10308 plate batteries, or 2
Eveready No. 486 or No. 770 plate batteries, or
2 Ray-0-Vac No. 9303 plate batteries. or
equivalent.
(C-l)—One 4 ½ volt negative grid bias or "C" battery. Approximate
size, 4 in. by l 7/16 in. by 3 1/16 in., such as:
1 Burgess No. 2370 negative grid bias battery,
or 1 Eveready No. 771 negative grid bias
battery, or 1 Ray-0-Vac No. 231-R negative
grid bias battery, or equivalent.
(C-2)—One 22 ½ - volt intermediate size plate battery, used as "C"
battery. Approximate size, 41/8in. by 2 9/16 in. by 2 ¾ in., such as:
1 Burgess No. 5156BP plate battery,
or 1 Eveready No. 768 plate battery,
or 1 Ray-0-Vac No. 5151 BP plate
battery, or equivalent.
5

INSTALLATION
Location of the Receiver. Radiola 25 may be located in any position
convenient to its user. It is well to remember, however, that large metal
surfaces such as radiators, piping, wiring or metal lath within the walls of the
building may absorb some of the energy of the radio waves. In modern
apartment houses or hotels it is therefore often advisable to locate the receiver
near a window. The best location can most easily be found by comparing the
operation of Radiola 25 in different parts of the room.
Remove two rubber wedges by pulling on them and
rotating drums downward simultaneously
Fig. 1. Removal of Rubber Wedges
Preliminary Preparations. Remove the two rubber wedges which hold
the Station Selectors from turning during shipment. Do this by pressing on the
rubber wedge and turning the corresponding drum toward you until the wedge is
released from under the metal plate. Keep these rubber wedges and replace
them, if the receiver is shipped at a later date, to prevent motion of the Station
Selectors.
Raise the lid of Radiola 25 to the vertical position, permitting the stay arm
to hold it open. Remove the red shipping clamp which holds the tube socket unit
during shipment, by taking out the four round head screws. When removing the
two screws which hold the clamp to the frame of the set, keep the nuts from
turning under the clamp and prevent their falling into the set. Inside the envelope
containing the instruction book will be found two shorter round head screws. Put
these into the two screw holes in the tube socket unit and screw them down
securely. Keep the clamp, screws and
6

nuts and replace them if the receiver is shipped at a later time, to
prevent the swaying of and possible damage to the spring-supported
tube socket unit.
Installation of Batteries. When making connections to the batteries,
do not permit the metal terminals on any battery connector to come
into contact with the terminals of other battery connectors, with other
battery terminals, or with the metal framework of the set, even for a
short time. Such connections cause rapid reduction in the useful life of
the batteries.
Remove Four Screws and the Red Shipping Clamp
Fig. 2. Removal of Shipping Clamp
Do not insert the Radiotrons into their sockets until the battery
installation has been completed. When making battery replacements,
push in the filament switch K (Fig. 13), and remove all six Radiotrons
from their sockets before proceeding to make the connections.
Make and keep all connections to the batteries as tight as possible.
Loose connections may cause objectionable noises or perhaps render
the receiver completely inoperative.
7

The battery connections described herein are also shown on the
"Instruction Card" fastened to the inside of the cabinet cover.
Place ”B” Batteries in Cabinet and Push Them Toward Front
Fig. 4. Location of 22 ½-volt "B" Batteries
NOTE.-Throughout this booklet, where two or more wires are connected to
a common terminal, the color identification of this group of wires is by means
of the color of the particular wire on which the metal marker tag is clamped.
8

To INSTALL THE 22 ½-VOLT "B" BATTERIES:Connect the batteries for
Radiola 25 as follows: Set one of the 22 ½ -volt plate batteries (see paragraph B-
l, pages 5 and 14) on the table at each end of the cabinet, and connect the four
cable leads according to Fig. 3. Place the batteries in the cabinet (Fig. 4), setting
them down upon the bottom next to the side, and then pushing them forward to
the front of the cabinet. On the left-hand side, lay the battery down upon its flat
side. The battery on the right-hand side of the cabinet may be placed in any
desired position.
Fig. 5. Connections to "C" Batteries
To INSTALL THE "C" BATTERIES:Place the two grid bias ("C") batteries (see
paragraphs C-l and C-2, pages 5 and 14) on the table to the left of the receiver,
and connect the pigtail of the 22 ½ - volt "C" battery and three cable leads as
described in Fig. 5. Now place the two batteries on top of the "B" battery already
in place on the left-hand side of the cabinet (Fig. 6) and push them forward to the
front of the cabinet.
9
Connect (-) 4 ½ C
(Black and Green)
to (-) 4 ½ Post
Connect (-) 22 ½ C
(Black with Green
Tracer) to (-) Post
Connect Red
Lead from (+) 22 ½
Post and (+) C (Green)
Lead to (+) Post

Place “C”Batteries on Top of Left-hand "B" Battery
Fig. 6. Location of "C" Batteries
To INSTALL THE 45-voLT "B" BATTERIES:Place the two 45-volt plate batteries (see
paragraph B-2, pages 5 and 14) in the two rear corners of the cabinet, and connect the
four cable leads as described in Fig. 8.
Place 45-Volt “B" Batteries in Rear Corners of Cabinet
Fig. 7. Location of 45-volt "B" Batteries
10

Fig. 8. Connections to 45-volt "B" Batteries
To INSTALL THE "A" BATTERIES:Place the six "A" batteries (see paragraph
A, pages 5 and 14) along the back of the cabinet (Fig. 9) behind the spacing rail
and between the two 45-volt "B" batteries just put in place.
Place Six "A" Batteries in Rear of Cabinet
Fig. 9. Location of "A" Batteries
11
Connect (-) Black to
(-) Post
Connect (+) 45 Two Maroon
and Red, One Black to
(+) 45 Post
Connect (+) 45 Maroon to
(+) 45 Post
Connect (-) One Yellow
with Red Tracer. One
Black with Red Tracer to
(-) Post

There will be found six pairs of leads coining out of the cable
just above these batteries, one of each pair being a short lead, the
other a long lead. Connect each of the short leads (+A) to the central
(positive) binding posts of their respective batteries. Connect each of
the long leads (—A) to the outside (negative) binding posts of their
respective batteries (Fig. 10).
After all the above connections have been made, it may be well
to examine them and to note that they all agree with the connections
illustrated in Fig. 13 and those shown on the "Instruction Card"
fastened to the cabinet cover.
Connect Six Short Leads to Center Posts and Six Long
Leads to Outside Posts
Fig. 10. Connections to "A" Batteries
Insertion of Radiotrons. All the Radiotrons should be handled
with care. Before installing the Radiotrons, turn the "BATTERY
SETTING"pointer F. Fig. 13, to "OFF," and push in the filament switch
K in the center of the vertical control panel.
Unpack the five Radiotrons, Model UX-199, from their cartons.
It will be noted that the Radiotrons have two small and two large
diameter pins. The Radiotrons should be so faced that the two small
sized pins enter the holes on the forward side of the sockets. Place the
Radiotrons UX-199 in sockets 1 to 5, starting from the right-hand
side, when facing the front of the set.
Unpack Radiotron UX-120 and insert it in tube socket 6 (the one
on the extreme left of the tube socket unit). It is important to locate
Radiotron UX-120 in socket 6 only.
12

Insert Five Radiotrons UX-199 in Sockets l to 5
Fig.11. Insertion of Radiotrons UX-199
Turn the "VOLUME CONTROL"' pointer P to "LOUD". Pull out the
filament switch K. Then turn the "BATTERY SETTING"pointer F
slowly to the right to 3.5. The Radiotrons should be lighted dimly,
the glow usually being just visible near the base of each tube. Note
that the Radiotron in socket 3 will not be lighted as brightly as the
others, unless
Insert Radiotron UX-120 in Socket 6 Only
Fig. 12. Insertion of Radiotron UX-120
13

the "VOLUME CONTROL"pointer P is turned to "LOUD". If the Radiotrons
light as just described turn the "BATTERY SETTING"pointer F to "OFF", push
in the filament switch K, and close the lid of Radiola 25.
F G H J K L M N P
Fig.13. Radiola 25 with Batteries and Radiotrons Installed
A Six "A" Batteries (see page 5)
B-l Two 22 ½ - volt "B" Batteries (see page 5)
B-2 Two 45 - volt "B" Batteries (see page 5)
C-l One 4 ½ - volt Bias Battery (see page 5)
C-2 One 22 ½ - volt "B" Battery used as Bias (see page 5)
D Stay Arm for Lid
E One Radiotron UX-120 in Socket 6 only
F "BATTERY SETTING" Pointer
G Left-hand Station Selector Drum
H First Stage Telephone Jack
J Two Filament Voltmeter Jacks
K Filament Switch
L Station Selector Drum Control
M Second Stage Telephone Jack
N Right-hand Station Selector Drum
P "VOLUME CONTROL"Pointer
R Five Radiotrons UX-199 in Sockets 1 to 5
14

Fig. 14. Insertion of Loop
Insertion of Loop. Unpack the loop for Radiola 25, which
conies in a separate container. Handle the loop with care, preferably
holding it by the center spindle to avoid damage to or stretching of
the wires. Push the projecting center spindle of the loop through the
loop socket hole (Fig. 14) in the top of the cabinet, rotate it slightly
until the contacts line up with the slots in the socket, and push it
down as far as it will go.
15

OPERATION
Clips for Measuring Filament Voltage
Fig. 15. Location of Controls
Loudspeaker. The phone plug of a Loudspeaker, such as
Radiola Loudspeaker Model 100 or Radiola Loudspeaker Model 104,
should be inserted in the second stage telephone jack (Fig. 15). The
first stage telephone jack may also be used for Loudspeaker operation
at reduced volume.
Filaments. Pull out the Filament Switch (Fig. 15). Turn the
"VOLUME CONTROL"to "LOUD." Turn the "BATTERY SETTING"control
to a position where good results are obtained. With new "A" batteries,
this point comes at about 3.5 on the scale. The life of the Radiotrons
will be considerably lengthened by setting the pointer of this control
as far to the left as practicable and then advancing slightly to improve
the quality of reproduction. This control may be advanced from time
to time as the "A" batteries grow weaker.
Voltmeter. In order to obtain the maximum useful life of
Radiotrons and batteries, it is recommended that a high-grade high-
resistance voltmeter be used to adjust the filament terminal voltage to
a value not exceeding 3.3 volts. This voltage may be measured by
inserting the leads of the voltmeter, preferably equipped with phone
tips, into the filament voltmeter jacks J (Fig. 13). With the "VOLUME
CONTROL"pointer at "LOUD"and "BATTERY SETTING"pointer at "OFF",
insert the voltmeter leads not more than one inch into the filament
voltmeter jacks, the lead from the positive ("+ ") terminal entering the
right-hand jack. Then advance the "BATTERY SETTING"pointer slowly
until the voltmeter registers proper value, which should be as low as
will give good
16

results and should never be over 3.3 volts. When the "VOLUME
CONTROL"is used to reduce the volume, the filament voltage will rise
slightly. If the filaments are then being operated with a voltage near
the upper limit (3.3 volts), it is advisable to turn the "BATTERY
SETTING"pointer slightly toward the left to compensate for this rise
in voltage.
Tuning. The tuning of Radiola 25 involves only the
manipulation of the two drums G and N on the Station Selector
Control L (Fig. 13), a simple operation after the principles described
below become thoroughly understood.
It will be noticed that on each of the drums there is marked a
scale for reading the positions of the Station Selectors. An arrow on
the center member indicates the setting. The settings of the two
Station Selectors should be very closely the same; i.e., if one is set at
60, the other should be at or near 60.
When moving the drums it will be seen that both of them will
turn if either is moved. By holding either of the drums stationary,
however, the other may be rotated independently.
When tuning for stations, the settings of which are not known,
proceed as follows: Set the left-hand drum G at about 10, and hold it
to prevent its turning. Rotate the right-hand drum N slowly back and
forth, around position 10, say from 5 to 15. If no signals are heard,
set the left-hand drum G at about 12, holding it to prevent turning.
Then rotate the right-hand drum N slowly back and forth around 12,
say from 7 to 17. If again no signals are heard, set and hold the left-
hand drum at about 14, and move the right-hand drum slowly back
and forth from about 9 to 19 If still no signals, repeat this process,
increasing the setting of the left-hand drum in small steps until the
whole scale has been covered.
The two station selectors must bear a particular relation to each
other in order to "tune in" broadcasting stations. After the first few
trials, it will be noted that when the two drums are properly adjusted
with respect to each other, a slight breathing sound will be heard,
even though no station is tuned in.
After hearing a signal, carefully adjust both drums for the
clearest reproduction. Once a station has been tuned in, do not
disturb the relation between the two drums. After this relation has
once been determined, the settings for the two drums should have
approximately the same relation for other stations. It will be
necessary only to rotate the two drums together by turning either one
of them. After other
17

stations have been located, however, it may be possible to increase
the volume and to better the tuning slightly by a careful
readjustment of the drums until the best reception is obtained.
If no signals are heard while tuning, various positions of the
loop should be tried. For every station there is a position of the loop
which will give best reception.
Control of Volume. As Radiola 25 is a very sensitive
receiver, it is usually necessary to use only a portion of its full
power. The loudspeaker output may be reduced by using one or
more of the following methods:
(1) Turn "FILAMENT"pointer to the left. This decreases the
volume by reducing the filament temperature, thus prolonging the
life of the Radiotrons. The pointer should, however, be set far
enough to the right to maintain a good quality of reproduction.
(2) Turn "VOLUME CONTROL"pointer toward "SOFT".
(3) Insert the telephone plug into the first stage telephone
jack H (Fig. 13).
(4) Rotate the loop until the best position is found.
(5) On powerful near-by stations an additional reduction is
often necessary. This may be obtained by holding the right-hand
station selector drum firmly in position and moving the left-hand
drum a few divisions either forward or backward until the desired
intensity is obtained. Note that the new position of the left drum
affects only the intensity or volume of the signal, while a slight
change in the position of the right drum affects the quality of
reproduction. Therefore the right-hand drum should be adjusted
with extreme care.
Interference. Signals from an interfering radio station may
be eliminated, or at least minimized, by either of the following
methods:
(1) While holding the left-hand drum G, rotate the right-
hand drum N forward or backward by approximately 10 scale
divisions to find another position of this control, where the
desired station will be again heard. The setting of the right-hand
drum nearer the 0 end of the scale is technically called the "lower
frequency peak," and the other the "upper frequency peak." Two
settings of this nature will be found for all broadcasting stations,
and the separation between them will be found approximately the
same throughout the whole length of the scale. It is recommended
that the right-hand drum N be consistently set at the "lower peak"
in the manipulation of Radiola 25. (When this is done, the gradu-
ations showing the settings of the right-hand drum will
correspond very closely with those of the left-hand drum.)
18

When interference is encountered, shift to the other "peak"
and use the one which gives minimum interference.
A station within easy receiving range operating at a
frequency below 680 kc. can usually be tuned in at four (instead
of the usual two) positions of the right-hand drum. This effect
occurs in normal operation of this Radiola and is not an
indication of any defect in the Radiola. It is recommended that
one of the two settings of the right-hand drum N, which
corresponds approximately to that of the left-hand drum G,be
used.
(2) Two distant stations on the same frequency may be
separated by rotating the loop, provided they are not in the same
general direction from Radiola 25. Set the loop on Radiola 25
where best results are secured, trying to locate a position where
the interference or undesired signals do not come in, but the
desired signals do.
Head Telephones. If it is desired to locate distant stations
with a pair of head telephones, the telephone plug may be
inserted in the first stage telephone jack (Fig. 15).
Calibration. The buff surfaces on the drums of the Station
Selector Control (see Fig. 16) provide a means for recording the
settings of the various stations. Once a station is recorded, the
drums may be reset at any later time to these positions, and if the
station is broadcasting and reception conditions at the particular
time are favorable, it should be heard. Before starting to record
these settings, the operator should become familiar with the
controls, and accustomed to tuning in stations. Records should be
made with a soft pencil and should be as small and neat as
possible, to permit the recording of the maximum number of
stations. Should the frequency assignments of the broadcasting
stations be changed, and should it consequently be desired to
change the markings, erasures may be made with a soft eraser,
using light pressure.
Note that in a few places throughout the country, par-
ticularly in the metropolitan areas, there may be two or more
stations assigned to the same wavelength or frequency, but
apportioned different hours of the day so that they will not be "on
the air" at the same time. Examples of duplicate frequency
assignments will be found in the "List of Broadcasting Stations"
in the rear of the pages of this booklet. Under such conditions, the
drum settings should be the same for both stations.
Station Log. The log sheets in the back of the book may be
used to record stations heard, if it is preferred not to mark on the
Station Selector drums or if a more detailed record is desired.
19