Philco 16 - Philco 16 Series Specific Troubleshooting Cases; Philco 16 Series Specific Distortion Cases; Philco 16 Series Specific Hum and Tuning Issues

11
Case Histories'~ of Receiver Troubles and their Remedies
Sec. 1
PHILCO 1', 168, HiX (Codes 1!5, 1!6)-(Cont'tl)
Distorted, _________ l)
open-circuiting, or change of resistance
of first audio tube 1-megohm screen re-
sistor
Intermittent
reception
2) replace 0.05-mfd. coupling condenser
No. 75 connected between first and sec-
ond audio
tubes
Distortion at _____ l) breakdown in 0.05-mfd. coupling con-
low
Yolume denser No. 75 connected between first
and second audio stages
Distortion at ______ l)
"open" 0.25-mfd. filter condenser No. 82
connected in plate supply circuit of 77
hich Yolume,
Weak "tinny"
sicnals
first audio amplifier '
Distortion _______ l)
center-tap of push-pull input transform-
er grounded to core or can (Insulate
from chassis with insulating bushings
and washers)
(crids of 42
tubes get red
hot)
Distortion _________ l)
leakage between insulation and chassis
of first filter condenser
(screens of 42
tubes get
red hot)
Whistling or _____ l)
insert a 700-ohm 1-watt carbon resistor
in series with the plate lead of the 78
r-f tube, and remove the condenser
shown in
the circuit diagram as No. 2A
squealing
2) check for "open" twin 0.05-mfd. conden-
sers No. 25. These are connected with
their "common" to ground, one to each
side
of tuning meter
3) check twin 0.0001-mfd. condensers No.
61. -These are connected with their "com-
mon" to ground, one on each side of the
second detector grid return load re-
sistor
4) solder pigtails from coil-mounting
screws of r-f, oscillator and i-f trans-
former shield cans to ground
lfotorboatinr .... 1) check electrolytic condenser block No.
sound rs, red, blue and blue 1-mfd. each, plain
2-mfd. Common negative connects to
can
Hum _________________ l)
Hum (intermit- .. 1)
tently)
check for "open" 0.3-mfd. condenser No.
97, connected across filter choke
check
for "open" 8-mfd. electrolytic filter
condenser No. 91
Dial sticks, __ l) excessive pressure exerted by felt rests
Dial slipa against dial
2) dial cable worn or frayed
PHILCO TH·U
Carrier hum _____ l) replace condenser No. lt with a 4-mfd.
at hirh electrolytic unit
Yolume
PHILCO 17
SH also Case Histories listed for Philco 15
Inoperatin ____ l)
check for "shorted" 0.05-mfd. condenser
No. 21 connected from oscillittor 11crHn
grid to ground
2) "open" tuning meter No. ti (indicated
by narrow shadow)
Inoperatin with 1)
Yolume con-
trol at mini-
mum settinc
and QAVC
switch at "on"
156
replace condenser 6 ( circuit diacram)
with a O.Ol-mfd-0.002-mfd. unit
(Cont'd)
PHILCO 17-{Cont'tl)
Intermittent __ l) check for "open" first audio screen re-
reception, sistor
Distortion 2) check for increased value in first audio
1creen
resistor
3) check for faulty by-pass condenser in
rrid-return of oscillator coil
4)
Intermittent -----1)
reception,
check for faulty r-f transformer
check the 2-mfd. section of the filter con-
denser block by-passing large 7,500-ohm
Cho
kine
wire-wound bleeder resistor
2) check the 0.5-mfd. condenser units by-
passing the 70,000-ohm resistor in the
1st audio plate circuit. They are mark-
ed B and C, respectively
Weak reception 1)
cassy type '5Z3 tube
Choked, __________ 1)
1-meg. carbon resistor in the plate and
screen-grid circuits of the silencing and
lit a-f tubes has increased in value,
thus lowering the screen-grid voltage of
I::;t a-f tube almost to the cut-off point
Distorted
reception
Distortion, ___ l)
secondary return of push-pull input
transformer grounded to metal case or
laminations internally
Hum
( control-grids
of output 42 2)
tubes glow
leakage between electrolytic filter con-
denser cans and chassis-due to seepage
and formation of oxides at the bases of
the condensers
red)
Hum -----------------1)
(stronc and
steady)
check for "open" condenser connected
across speaker field
Whistling ---------1)
( intermittent
check for "open" 0.05-mfd. condenser
No. 21 connected from oscillator screen
grid to ground
or steady)
Apparent _________ l)
check for loose rivets which hold the
bakelite insulating panels in the sides
of the tuning condenser sections, permit-
ting the statprs to shift
"fading" due
to freqµency
drift in
receiver
PHILCO 17-X
Distortion, ____ 1)
1st tilter condenser leakai-e between in-
sulation and chassis
Type '42 1creens
get red hot
Hum ------------------1 )
(stronc and
steady)
check for "open" condenser connected
across speaker field
PHILCO 18 (Codes 122, 123)
Inoperatin __ l) control grid of type '75 tube shortinr
to shield can
2) open-circuited audio coupling-condenser
I
3) "aborted" tone control condenser
4) check first i-f primary for "open" or
high-resistance joints
5) check A VC coupling condenser for
"open" or "intermittent" joint
6) check for "shorted" 0.05-mfd. condenser
No. 12 connected from tuning to ground
( wide shadow)
7) check for "shorted" electrolytic filter
condenser
No. 40 (capacities 2-1-mfd.,
1-2-mfd.
(narrow shadow)
8) check for "open" tuning meter 'No. 63
(narrow shadow) .
9) check for "shorted" 0.05-mfd. condenser
No. 20 connected from 6A 7 tube space
charge grid supply filter resistor to
cround
10) check for "shorted" · 0.006-mfd. con-
denser No. 4~ connected from plate of 42
flrat i-f tube to ground
11) check for "open" primary in input
transformer No. 41
(Cont'd)