Technical information

O
RADIO
RETAITING'S
"Seutie
RADIOLA
I7
No reception
look
for
open
section
in
voltage
divider
located
on
chassis sub-base
of
socket
power
unit.
From
where
output
of rectifier
feeds
into
divider, value
of sections in
their
order
are 580,
4,000,
2,500,
200
and
1,900
ohms.
RADIOLA
t7
Bad
hum
that
cannot
be taken
out
by
hum
controls
. . . shorted
6lter
choki:
replace.
RCA
R-t7-M
(G.
E.
BX)
Hum,
no
reception
cl-reck tubu-
lar
electrolytic
condensers
for
open
or
decreased
capacity.
Oscillation
rvith
signals
heard
in background
also
caused
by satne
trouble.
RADTOLA
t7, r8,
s0
Erratic
action
of volume
control
at
maximum
and minimum
settings
.
movable
arm of
control
jumps
over outer
terminals
due
to springiness
of
arm.
Remove
chassis
from
cabinet
and bend
outside
terminals
of
control
up
sufficiently
so arm
cannot ride
over
them.
RADIOLA
17, 18, 50
Repeated
breaking of
condenser
drive
cable
.
Due'
to scraping
of
cable
on
edge of drum. Install
new cable,
rotate
control knob fullv
in one direction
and then
the other
siveral times.
If
scraping is noted
remove
dial
scale from
drum and
file edges to assure
better
cleanance. When replacing
scaie
put
it
slightly off
center,
more
toward
the
edge
of the drum on which no
filing has
been
done.
RADIOLA
17.
50
Unstable
. scr-ew loose
on termi-
nal board making poor
contact. Tight-
en
all
scrervs.
RADIOLA
IE
Oscillation
when new
tubes are in-
stalled
.
.
.
locate
neutralizing
condenser
under
chassis and
turn counter
clock-
wise
till oscillation
ceases.
RADIOLA I8 D.C.
No
plate
voltage
. .
.
Open
1,000
ohm
plate
resistor located in
power
unit.
Con-
nect a 20-watt, 1,000
ohm replacement
from binding
post
7
to binding
post
9
for
permanent
repair
without necessity
of
removing
and replacing
chassis.
RCA
RE-20
Tone
control
noisy,
volume
decreases
in bass
position
replace
small
choke in metal
can
located
below
chassis.
A,s
this choke may
be difficult
to obtain
it may
be replaced with
a midget
filter
choke.
48
VICTOR RE
20
Loud hum open
.1
mfd condenser
from
cathode of. 27 second detector to
one
side
of
]
watt 1 meg resistor.
This
condenser is in condenser
pack
and
has
two blue leads.
Oscillation
over
entire dial . . . open
.002 mfd 400 volt
condenser
from
plate
of
second
detector
to
cathode.
RCA.VICTOR
R-21
Low
hum,
stl'oug ntotorboating
when
the,l7
behind
the 80
rectifier
is
rernovetl
. one
megohru
resistor
f ronr
ter-
nrinal
3 on
phono
terminal
strip
sl-rort-
irrg
to ternrinrl
-1.
To
test,
sliort ter--
rninal
3
and
4
rvith sct.cw-driver.
If
hum
cloes not
increase
the
troub'le is
:rt
this
point.
RADIOLA
R2I
Xlotorboating
. . . Check
I
nrfd
con-
dcrrscr (C14
in
diagram)
which by-
passes
the
screens
of r.f., first detector
and i.f.
RCA D-22-l
Yolumr
Erprndrr
Lack
of expansion, drop in volume
when
expander
is
turned
on . . re-
place
part
#11608
consisting
of two
I mfd
and
one
4 nrfd
condensers. These
are
C-208,
C-2@,
and, C-210
in the
schematic. Also
check
R-203. a 100.000
ohm resistor in the
plate
circuit
of the
6L7 lor
drop
in
resistance. If
opera-
tion
still unsatisfactory
check
C-201,
C-202,
and C-206.
Excessive
hum
with switch in
phone
position
can be
remedied
by
replacing
C-106. an
18 mfd
condenser
(part
#11496)
in
the
plate
circuit
of the
6C5
first
audio stage.
R.ADIOLA 21, 22.
Apparent short
be-
tween red
and
maroon
B
plus
lead
and
chassis. If
short develops when tube
is
inserted
and disappears
when
the
tube
is removed from 22
sockets
look
at
plate
prongs
to see if these touch chassis.
Screws
holding
sockets down loosen
due
to soeaker
vibration and sockets shift.
RCA R27
Irrsensitive
connect
a.01 nticl
conrlerrscr
{r'our pl:ltc
to terrrrinal
to
glid
tr:rnriual
on
tlrc r.i.
coil.
RCA
n27
Speaker
rattle
after a
few
months
of
use
.
.
Remove
set from
cabinet
and
glue
two
pieces
of
cork at
top
and
bqttom
of
place
wtrere speaker
cone
comes.
These
shor:ld be
just .thick
enough to
come
in
contaot
with
the
cone,
forcing
it back
slightly.
RCA R-28.
Speaker rattle,
sounds
live
voice
coil
striking
pole,
but
is rarely
this . .
. Cone
is
screwed to speaker frame
only
at
bottom, allowing
top
part
to
vibrate
against
frame
on loud signals.
Screw top edge of cone
to
frame
with
short
4/36
machine screws
and nuts.
Holes are already in frame,
so no
drilling
is required.
RCA
26
A.V.C.
action weak,
noisy.
.
. . Check
a.v.c.
plate
choke. Also
check
C
18.
C 20,
C
2l for
shorts.
RCA
R28.
Loud
"putting"
noise
despite
good
tubes,
correct
voltages
Caused
in
many
cases
by oscillating
mixer
sectiol
of.
247.
Remove
wire feeding
screen
voltage
to thi^ tube
section and insert
an
r.f.
choke in
series, bypassing from
the
screen to
ground
with
a .5 con-
denser.
RCA
VICTOR
R-28-P.
Set oper-
ates
ok on
broadcast
but
is dead
on
shortwave
band
.
Look
for
shorted
trimnrer condensers
on band-change
switch. Mica frequerrtly
breaks.
RCA R.28P
Noisy
. .
.
<lefective r.f.
coil nrountecl
irr
shield on top of clr:r.si..
RCA R2EP.
Violent
oscillation
all
over
dial
. . Probably an open cir-
cuited 4
microfarad
electrolytic screen
by-pass condenser.
It is mounted under
the
chassis
in a common container with
a second 4 mike
unit.
Chanee
both to
prevent
a call back.
RCA
R-28. R-2E
lW
Oscillation Replace
two
mfd.
screen
and
plate
voltage
bypasses.
RCA
R28,
R28P
(cE
K50,
KsoP).
Noise,
sounding
like
loose
connection
. .
. Probably
one
of flexible
leads
of
the
57
plate
choke
rubbing
against
green
500
ohm 2A5
cathode
resistor
beiveen
r.f.
choke
and rear
of
chassis.
Gurgle
and
squawk
after
tubes
heat
. . .
prJU-
ably
open
filter
block.
(LF.
175
kc.)
RCA
M30. Faulty
control
of volume
.
Usually caused
by change in re-
sistance
of carbon
unit
located in re-
mote
control
box. The
correct value is
70,000
ohms. Check
the volume
con-
trol resistance
before installing
the
car-
bon
unit as its value
may have
changed,
necessitating
some compensating
dif-
ference
in
the fixed
unit. The
cotrol
should
check at 50,000
ohms.
Use a
slide resistor
to
determine
the correct
total resistance.
RCA I{30.
Lack
of con.rplete
rnanual
volurne
control
is
usually
an indication
of
trouble in
the a.v.c.
circuit-
RCA
M-30
No control
of
volunre
reolace
grcrn
$ilc
in
c;rlrlr lluLl rtrrrs
fronr
.et
to
coutrol unit.
RCA
30, 30A.
Burned
out 876 bal-
last
tube
When customers
ref use
to
spend money
to replace
it
wire two
!"-p
sockets
in
parallel
in
its
place.
Place
a 75
watt electric
bulb in one
and
a
100 watt
size in
the other.
vtcToR
R32
Normal
except for loud
hum
suspect
the 20
ohm
resistor
across the
heater
of
the 27.