Philco 28 User manual

PHILCO
1ro.v.a.••T.on
Serviee Bulletin-No. 203
Model 28
Philco Model 28 is a s~-tube receiver operating on 115 volts, either alternating current (A.C.) or
direct current (D.C.). It is capable of receiving either standard and police broadcasts between 540 and
1720 kilocycles; or short-wave stations between 4.2 and 13 megacrcles. The left-hapd side of the dial is
calibrated in kilocycles for standard reception and the right in megacycles for short-wave stations. A
two-position switch changes reception from st:i-ndard to short waves.
Model 28 uses a type 6-A-7 detector-osc1llator, two type 39-44 I. F. Tubes, type 75 2d detector,
type 43.output. tube , and type 25-Z-5rectifier .. The power consumption is 50 watts .. The intermediate
frequency is 460 K.C ,
On Line Voltage 120 AC TUBE SOCKET VOLTAGES On Line Voltage 120 D.C.
TYPE TtraE 6-A-7 39-44 39-44 75 43 25-Z-5 6-A-7. 39-44 .39-44 75 43 25-Z-5
--- --- -- --- --- --- -- ---
Plate (P to K) ... . . . . 100 100 98 45 95 120 95 95 85 40 90 ..
--- --- -- --- --- --- --- ---
Gl =-8 Gl-;;slO
Screen Grid (SG to K) G2=80 100 100 .. 100 .. G2=80 95 95 .. 95 ..
G3&5=60 G3&5=60
Total Filament Voltage-75 Total Filament Voltage-83
Hi~h resistance D.C. voltm eter used for above tests. Volume control st maximum; dial st 55; wave hand switch at left. Refer to
Fig. $~n~~kllo~i:tJ25 Circuit Test er is recommended for making the -above volta ge test,,
Fig. 1-T op View Showing Location of Compensating
Condensers.
TYPE25-z.!i
RECTIFIE~
TYPE15
TYPE6*7
0ET.OSC.
2•0.,oer,l'!A.F. 2•0.1.F. 11T.t.F.
Fig. 2- Bottom View of Sockets for Testing Voltages.
Adjusting Compensating Condensers
For adjustment of compensat ing (padding) condensers in
Model 28, an accurately calibrated signal generator, an output
meter, and a special insulated padding wrench and screwdriver
are needed. We suggest the Philco Model 024Signal Generator,
which is accurately calibrated and easy to handle. Philco No.
3164 fibre wrench and No. 27-1159 fibre-handled screwdriver
are also recommended. For the output meter either Philco
Model 025 complete tester or Philco Model 012 shadow out-
put meter is suggested.
The chassis must be removed from cabinet in order to make
all adjustmen ts.
Adjustments are made in the following order--
ADJUSTMENT OF THE INTERMEDIATE FRE-
QUENCY-Rt:move the grid clip from the type 6-A-7 tube
and connect the" ANT" output terminal of the signal generator
to the grid cap of the tube. Connect the "GND" terminal of the
signal generator to the "GND " terminal of the receiver chassis.
Connect the output meter adapter leads to the plate and
cathode prongs of the type 43 tub e. Set the signal generator at
460 K.C. (the intermediate frequency of Model 28) and with
the receiver and signal generator turn ed on, the wave band
switch at left and dial at 600 K.C., adjust each of the I. F. com-
pensating condensers in turn, to give maximum response in the
output of the receiver. The three pairs of I. F. compensating
condensers are located one pair at the top of each of the three
I. F. transformer shields. These are the three metal "cans" near
the rear of the chassis. Each of the transformers has a dual
compensating condenser mounted at its top, and accessible
through a hole in the top of the coil shield. In the dual compen-
August, 1934
sators, the Primary circuit is adjusted by turning the screw; the
Secondary circuit is adjusted by turning the hex-head nut.
ADJUSTMENT OF THE WAVE TRAP-Replace the
grid clip upon the Detector-Oscillator tube (Type 6-A-7).
Connect the output leads from the signal generator directly
to the antenna and ground terminals of the receiver. Set the
Wave-Band Switch of the receiver to the standard broadcast
band (left-hand position) and the Station Selector at the low
frequency (540 K.C.) end. Adjust the Wave Trap condenser
to give MINIMUM response to a 460 K.C. signal from the
signal generator. The Wave Trap ® is located at rear and
underneath the chassis, and is shown in Figure 1. It is reached
from the rear of the chassis by inserting the fibre wrench
through the hole near left-hand rear corner of chassis.
ANTENNA AND OSCILLATOR "HIGH" AND "LOW"
FREQUENCY ADJUSTMENTS-The "antenna" and "os-
cillator H. F." compensators are located on top of the tuning
condenser assembly, reached from above.
Set the signal generator at 1500 K.C ., tune in this signal on
the set and adjust the antenna compensator® (nearest tuning
control) to give maximum reading in the output meter .
Next adjust the oscillator H. F. condenser @ (located on
the other section of tuning condenser) to maximum reading.
Finally, set the signal generator at 600, tune in this signal
and adjust the "oscillator L. F." condenser, located under-
neath chassis (@in Fig. 1) to maximum reading. This adjust-
ment is reached through the hole in top of chassis, between
the two electrolytic condensers (left-hand end of chassis when
facing rear).
Printed in U.S.A.
philcoradio.com

®
,-- ---t-1}
"
I.F.•460 KC.
Fig. 3-Sc hem at ic Wiring Diagram
REPLACEMENT PARTS-
MODEL 28
No.on
Flis. Description Part No. Llat Price
Each
I
Cf)
Condenser (.00125 mfd.-Mica) . . ...... ... ...... 58S6
Wave:Trap . ...... . ... ...... .. .. . ... ... ... .... 3/HI050
Resistor (10,000 ohms) (Brown-Blo ck-Orange) .... 33-1000
Antenna Tr ansformer . . ........ ....... . ... ... .. 32-1360
Wave Band Switch .... ..... . .... . . .. . ......... 42-1062
Conden,er (.25 m!d.-Tubular) ........ . ..... . . .3()-4146
Tunin g Conden ser A!!embl;v. . .... .. ..• . . ..... .31·-1366
Compensating Conden ser (Antenna). . . . . . . . . . . .Part of CD
Condenser (.1 rnfd.-Tubular) . ..... ...... .. .... 30--4122
Resistor (400 ohms-Flex .) (Yellow-Black-Brown). 33-3016
Cond enser (.1 mfd.-Tubular ) ......... . ........ 3()-4122
Resistor (120.000 ohms) (Brown-R ed-Yellow).... .33-1128
Condenser (.003 mld .-Mi ca) . . .. . .............. 30-1028
Compensating Condenser (Osc. H . F. ) .. . . .. .. . .. Part of CD
Oscillator Tra nsformer .............. .. . ........ 32-1361
Condenser (.0008 mld.-Mi ca) ... . .... . ......... 5878
Resist.or (10,000 ohms) (Brown-Black-Orange) .. . .3524
Compensating Condens er (Osc. L. F .) ........... 04000S
Comp ensatin g Cond enser (1st I . F . Prim ary) ... . .Part of @
First I. F. Transformer ....... . ..... .. . ... ... . .32-1362
Compensating Condens er (1st I. F Secondary) ... . Part of@
Resistor (200 ohms-Flex. ) (Red-Black-Black) ... .7217
Condenser (.1 mfd.-Tubnl ar) .. . .. . ........... .3()-4122
Condenser (.09 mld.-Twin -Bakelite Block) . . ... .4989M
Resistor (15,000 ohms) (Brown-Gr een-Orange) •... 6208
Resistor (.1 meg.) (Whit e-White-Orange) ...... .. 4411
Compensating Conden ser (2d I. F. Primary) •. . •. .Part of@
2d I. F. Transformer ... .... .. ...... .... . .. .... 32-1363
Compensating Condenser (2d I. F. Secondary) ... .Part of@
Compensating Condenser (3d I. F . Primary) .. . ... Part of@
3d 1. F. Transformer ...... .............. ...... 32-1364
Compensating Condenser (3d I. F.
Set-ondary) ........ . ...... ..... .Part of@
@
8 Conde nser (.05 mld .-TubularJ ..... 3()-4()2()
@ Resistor (1000 ohms) (Brown-Bla, ·k- .35
Red) ....... . ... ............... 5837
~ Resistor (2 megs.)(Red-Black-Green) 5872
@ Condenser (.0001 mfd.-Twin-Bak,-
lite Block) ....... . .. . ...... ·.... 8035E
@) Resistor (50,000 ohms) (Green-
Brown-Orange) .............. ... 4518
@) Volume Control and On-Off Switch
(350,000 ohms, tapped at 75,000).. 33-5066
@ Resistor (10,000 ohms) (Brown-
Black-Ornn ge) ................. 33-1000
i
~
43
Condenser (.05 mfd .-Bakelit e Block) 3615- BU
~ Condenser (.01 mfd.-Tubul nr) . . .. .30-4124
Condenser (.00025 mfd.-Mica) .... 5858
Resistor (1 meg.) (Brown-Black-
Green) . ..... . ...... ..... . ... .4409
@ Resistor (.5 meg.) (Yellow-Wbite-
Yellow) . . .. ..... .. ... .. . ...... 4517
ICondenser (.1 mfd.-Tubulnr) .... . .3()-4122
46 Condenser (.25 mfd.-Tubular ).. ... 3o-4146
47 Condenser (.00011 mfd.-Mi caJ... .. 30-1031
@ Condenser (.0'2mfd.-Mi ca) . . ... .. 30-4113
@ Resistor (.25 meg.) (Red-Yellow-
Yellow) ... .. .. ............. . .. 4410
@) Resistor (.5 meg.) (Yellow-White-
Yellow) ... ... . . ........ . .. .. . .4517
.25
.25
.25
.25
1.45
.25
.35
.25
.35
.25
.25
.35
.40
.35
.30
.25
.25
S0.35
.50
.25
.60
1.10
.40
5.70
.35
.20
.35
.60
.65
.65
.35
.25
.35
1.50
.20
.35
.40
.25
.25
1.50
1.55
i
2
63
65
I
Resistor (50,000 ohms) (Green-B rown-Orang e) ... .4518
Condenser (.09 mfd.-Twin-Bnkelit e Block) . ... ... 4989M
Resistor (25,000 ohms) (Red-Green-Orange) . .. ... 33-1013
Tone Contro I (3-point)........ .. . .. . ........... 3()-4211
Condensers (In tone control) ..... . .....•...•. .. Inside @
Output Transformer (28CJ . ... ... ..... .. . . . .... 32-7243
Cond enser (.25 mfd.-Tubu hr) ................. 3()-4146
V . C ·1 d C A bl lP-21. ... .. ...... 02861
oice 01 an one ssem y K-27 .••.•. .. . . .36-3159
Field Coil and Pot Assembly P-21. · · · · · · · · · · .3&-3357
K-27.. ...... . .. 36-3352
Pilot I.amp . . ... . ............... . .... .. ....... 4567
Resistor (Wire Wound , New Type)(37 , 63, 29 obms)33-3!59
Filt er Choke .............. .. .. .. . . .. ... .. .. ... 6658
Filter Choke ... .... . .. . . . ... ..... .. .. . .... . ... 32-7018
Condenser (.05 mfd.-Tul,ular) . ..... .......... ,3()-4123
Conden ser (Electrolytic 6 and 12 mid., 150 volts) .. 30- 2083
Resistor (Wire Wound , New Typc)(lO, 137 ohms) 33-31 58
Condenser (.09 mfd.-Tubular) .......... ... . ... 3()-412:l
Condenser (Electrolytic 6 and 12 mid ., 150 volts) . .30-2083
Five-prong Socket ... . ............ . ...... .. . . . .7546
Six-prong Socket .... . . . . ....... .. . ......... . .. 7547
Seven-P.rong Socket . ..... . .. . . . ... .. . . ....... . .27-6005
Knob (large) . .... .......... . . . . ............. .27-4051
Knob (small) ... . .. ... ............ . ...... . .... 27-4052
Dial Assembly ....... . ..... . ..... .. ..... . ..... 31-1208
Speaker So,,ket (Ezcept 28C) ........ . ... . .. .. .. 4957
A.C . Cord and Plug Assembly . . . .... . . .. ....... lr943A
Chassis Mounting Screw . ........•. . ..... .. . . . .W-134,5
Chassi s Mounting Washer .. . ...... . ..... . ...... ~2089
Chassis Mounting Foot. ... ...... . . . ... . . . . .... 27-4116
Chassis Mounting Foot Plate ... .. ........... . .. 27-7497
Back Cover (28-C only) ..... . ...... .. ... ... . . .. ~2006
Bottom Shield Plate. . .. . . . . .. .. . .. . . . .. .. . . .W-200li
S0.25
.40
.25
.75
1.10
.40
.65
.80
3.50
4.00
.35
1.50
1.50
.35
1.70
,45
.35
1.70
.11
.11
.11
.10
.10
.45
.10
.60
2.75C
.35C
.05
.35C
.50
.30
+
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