Technical information

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RADIO
RETAILING'S
"Sqzuie
llo
RCA 96T4.
96T5. 9616
Pushbutton antenlla
trinrruers rvill
not
tune look for
sholt to livet
between back to
'back
band srvitch
terminals. Both are indicated as
8
in
the diagram although there should be
no
electrical connection.
RCA TMV-97-C.
When
using this oscillator
be
sure
the shielded
lead
from
the output
con-
nection
is
fabric-covered or the
B-
battery
will run
down
in the
event
the
shielding
touches
the
outout
iack.
RCA 98K
Line
noise
when tuned
autouratically,
decreases when
"dial
turniug"
buttorr
is
pressed
Noise
is induced
into
RCA
98K
Line noise
when
tunecl
a-utonraticallv.
decreases
rvhen
"dial
tulnirrg" button
is
pressed
Noise is induced into
set by nrotor
lvinclings.
Connect .01
mfd 600 volt conclenser
frour extrenre
right hancl ternrin;rl
of
tuning su'itch
to
cl-rassis.
RCA
VICTOR r00
Low volume
leaky antenna
coupling
condenser
which
blocks
the
a.v.c.
action.
Replace with
similar
higher
voltage
unit.
RCA f00B
SPEAKER.
Burned out
coil
Re-wind
bobbin full
of
No.
26
d.c.c.
copper
wire, then
use a
dynamic
speaker
output
transformer
with
a low impedance
secondary.
This
will
give
improved
tone and
volume.
RCA Mtot,
Mto.t, Mtor,
Mr09
Noisy
Replace
leads'
f
ron:
stators
of condenser
gang
to
grid
caps.
RCA
f02.
Line cord burned
out
. . ,
When
replacing with new cord be
sure
to roll a
piece
of
mica over the
re-
sistance
asbestos and tape,
allowing mica
to be
tr
in. larger than
the resistance
wirc.
This
wire
runs to the socket
of
the
37 and
when
set is moved around
the socket
lug
frequently
cuts into the
asbestos, shorting
the
wire.
Mica
goes
into
the set
under the
socket.
Tape
ot
tie
tine cord
so that
it stays
fastened
to
the chassis.
RCA 106. The a.c, model can be used
with single
pentode
output
tube models
with co':siderable improvement
in tone.
The field is about
450
ohms. Use
it as
the
bias resistor.
RCA M IO9
Dead
irom
550
to 900 k.c.,
rveak on
remaining portion
of dial . .
. Open
100
ohm resistor
in
antenna filter.
This
resistor
along rvith
a
choke and
con-
denser are contained
in
a small
metal
can located
at
a
point
rvhere
the antenna
enters tlre chassis.
Remove
can
and
replace
resistor.
52
RCA llO.
Tracking
condenser
showr'
on circuit
diagram as
number C-31
ap-
pears
to
be
missing . . .
This condenser
has a
minimum of
15 and a
maximuh of
70 mmf.
Try inserting one
small
enough
to be
placed
between
oscillator
coil and
chassis. Adjustment
to
about 50
mmf.
will
give
maximum
deflection
at 600
kc.
white
rocking tuning
condenser.
Sen-
sitivity will
be uniform
over
entire dial.
Apparently this
condenser
is
occasion-
ally omitted through
error
in
production.
RCA
I tt,2t t.
Intermittent operation or fading
.015
coupling
condenser
C28
partially
opens.
In later
production
this
is a .02. Re-
place
with
.02,
600
volt.
Connects
f.rom
42
grid
to
6B7
plate
and
is located
under
main
resistence strip. Align
at 460 kc.
RCA il8, 2rl
Distortion,
all
voltages
check
with
service sheet.
. .
.
Replace cathode
filter
in 687.
RCA r20
Distortion, circuit
and
voltages
check
O.K. .
Connect
a
150,000
ohm
re-
sistor
between
yellow lead on
volume
control and
common
screen
circuit.
This raises the
bias
on the
687 slightly,
reducing
plate
voltage
drop
in
plate
coupling
resistor.
Oscillation
when
volume
is increased
check screen
bypasses and filter
from
Bx to
ground.
RCA r20
Oscillates
when
aligned
. .
replace
cathode
bypass
on
58
r.f.
rvith
.25
mfd unit.
RCA VICTOR t20
Motorboating, no signals
. . .
. check
for open condenser
in three
section
electrolytic
block located
to right of
gang
condenser.
The offender
is usually
the screen
grid
bypass.
RCA l2l.
Motorboating
UPen
4 mike section of
capacitor
pack
(I.F.
l/J l(c.).
RCA t2l
IGE
KJ4)
Motorboating
. . .
If fingertip
on
control
grid
of rearmost
58 stops
oscilla-
tion,
remove red
tead coming from
C-28
in
3
section electrolytic
pack
and
replace.
with
single 8 mfd.
unit.
RCA r28
\\'e:rk,
distorted
4 nrfd cathode
l.rypass
t.rtt 6BZ
leakirtg- or sholted.
RCA-VICTOR
t40. t4l
Code
interference
. install
wave
trap in
antenna
circuit.
One can be
made
from
old 456
k.c.
transformer.
R.Ct. VlcToR t.f3
Noisy, internrittent
hum
: . replace
500 ohnr cathodo resistor
on
76
tube.
RCA
r,r3, 242
Periodic
hum accompanied
usually
by
distortion
Replace
(C45)
cathode
bypass
on first audio
with l0
mfd.
50 volt
unit.
Also replace
(C46),
a
4 mfd.
450 volt
electrolytic
connected
from
same
cathode
to B
plus.
RCA 22 |
Hunr, especially
on stations
open 4
mfd condenser in
pack.
Con-
nccts from
R6 (20,000
ohms)
to
erouncl.
RCA
221
Bad
hum . . .
leaky 4 mfd.
cond.
in
capacity
pack,
No.
6703-C 22, dis-
connect
blue lead
and
replace.
RCA 233
Ballast
tubes burn
out
quickly
replace
ballast with 125
watt house
lamp.
This
is a 32 volt set
and will
receive
the correct filament
voltage
when
the
125
watt
lamp is
substituted
for ballast.
RCA
2{tB. Intermittent
reception
. Corrosion where
leads
are
welded
to
coils, both input and output
trans-
forlners.
RCA VTCTOR
260
Internrittent
fail:re
of .05 nrfd
:r.v.c. filter
courlenser in
thc
r.f.. first
detector,
and
r.f.
RCA VTCTOR 261
Distortion, weak signals.
Look
for
60,000 ohm
I watt
plate
resistor
overload.
Usually caused by
leaky
or
shorted
4 mfd
condensers
(red
leads)
located in
capacitor
can
and
connec(ed
to
each
end of this
resistor. Replace
resistor with
a
2 watt unit,
connect two
new 4
mfd.
dry electrolytics
in
place
of
suspected condenser,
after clipping off
red
leads close
to can.
RCA 262,
G.
E. Mr07
Crackling
noise
.
. Check
push-pull
audio transformer between
driver
and
output stage by
imposing
an
eclual
load
on each
plate
lead of the transformer.
Low voltage
on one
lead will indicate
defective
winding.
Replace
transformer.
RCA 28t, 262
I.I;.
rvon't
hold alignnrerrt solder
leads
from r.f. transforrner
to
insulated
eyelets
through
which
they
pass.
Oscillation on
high
f
requcncy
end
rvith sensitivity
control
advanced
leplacc
i.f. cathorle and screen
bypasses.