PHILCO
ltEO. U.S. PAT, OfF
Service Bulletin No. 166-A
Models 38 and 38-A (Code 123)
The Philco Models 38 and 38-A are battery-operated
five-tube superheterodyne receivers. Model 38 is design ed
for use with a two-volt storage battery for filament ("A")
supply; Model 38-A for use with dry "A" batte ry,- in
conjunction with a Type lAl ballast tube. The frequency
range is 545 to 2415 kilocycl es, and a wave-band switch
permit s the selection of eithe r the standa rd broadcast or
police and amateur radio station s. Models 38 and 38-A
possess receiver chasses that are identical. When shipp ed,
Model 38 has a
shorting jump er across the filament con-
tacts of the Type lAl Ballast Tube socket. This shou ld
not be disturbed as long as the receiver is operated upon
the storage batt ery. Removal of it will open the filament
circuit. The Model 38-A,-in add ition to its complement
of five tubes,-is equipped with a Type lAl ballast tube
which
must be used with the receiver operating on dry
"A" battery. A special resistor is used across the filament
of the Type lAl ballast tube .
The Models 38 and 38-A employ a Philco Type 1A6
tube as det ector-oscillato r, a Type 32 tube for the inter-
mediate frequenc y amplifier, a Type 32 as second detector ,
a Type 30 tube for the first audio frequenc y stage, and a
Type 19 tube as output (class
"B" amplifier ). The se are
the Philco low-current drain two-volt tubes.
The Model 38 is designed to be used with the Philco
Type 172-R two-volt sto rage battery and Philco Type
"P-9068" "B" /"C" battery; the Model 38-A with
thr.
Philco Type "P-896" dry "A" battery and Philco Typ e
"P -9068" "B" /"C" battery.
Tube Socket Voltages
All Voltages Measure to Ground or -F
32
1A6
32 (I.F.)
(2nd
30
19
Det.)
Plate ....
12i 12i
.50
126
126
Screen
G2
82
Grid . . .
Gau 64
64 22
. . . . ....
Grid .....
G1
- 10
. . . . . . . .... G1 -2.9
G2 -2.9
FIG. 2-Bottom of Chassis Showing Parts;
and
Sockets for Testin~ Voltages
The filament ("A") supply should never exceed two
volts at the tube socket termin als of either Model. The
Type lAl tube acts as a
voltage-regulator, and maintains
a constant "A" potenti al to the filaments of the Model
38-.
.\.. The filament current drain upon the "A" batter y is
720 milliampere s. The "B" batt ery curre nt drain varies
between 8 and 12 milliampere s,-a t 135 volt s. The inter-
mediate frequency of the superheterodyne circuit is 460
kilocycle s.
FIG. I-Locations of Compensating Condensers
NOTE: Compensators ®and@) are shown as viewed from
top of chassis ; all others in position seen from bottom.
Adjusting Compensating Condensers
Adjustment , of compensating cond ensers in Model 38
requires the use of an accurate signal generator (such as
the Phil co Mode l 024), an output meter (Phil co Mode l 012
or
02:j are recommended ) and a special adjusting wrench
(Philco No. 3164). Th e
I. F. or intermediate frequency
of the set is 460 IC C. Refer to Fig. 1 for locations of
compensating condensers.
.l. F.-Set signal generator at 460 K. C. Remove grid clip
from cap of 1A6 tube
and connect antenna lead from
signal generator to cap of tube, connect ground lead
to ground post of set. Set dial of receiver at 550 and
wave hand s"·itch rit left . See that set is connected
to
lmt.teries and volume contro l full "on ." Connect
output meter
to primary terminals of output trans -
former (in chassis). Turn "on" the receiver
and signal
generator.
Adjust the four I. F. compen sat ing con-
densers
@, @, @ and ® to give maximum
respo nse in the output meter. The se adjustments are
all made from the rear of the chassis through holes
in sub-base .
. \ :'\T. II. F. and OSC. H. F. (standard wave )-The se are
condensers ® and @) located on top of the tuning
condenser assembly and adjusted from above.
® is
the one nearest the front of chass is.
Ret signal gene-
rator at 1500. Replace grid clip on cap of
lAG tube
and connect antenna and ground leads from signal
generator direct to antenna and ground posts of set.
Turn dial of set to 150 and adjust condensers
® and
@) for maximum reading in output meter.
OSC.
L. F. (standard wave)- Set signal generator at 600
and turn dial of set to 60. Adjust condenser
@,
reached from rear of chassis, to give maximum read-
ing in output meter.
A~T. H. F. and L. F. (police band )- Turn w:we band
switch to the right . Set signal generator at 2400 and
dial at 2.4 (lower scale). Adjust condenser
(J) to
give maximum response in output meter. Now turn
dial to 1.5 and set signal generator at 1500. Adjust
condense r ® for maximum response. Condensers
® and (J) are reached through the two holes in top
of chassis to rear of tuning condenser assembly .
. :i°OTE: If readi ng on output meter is too great during ad-
jnstment~, turn
down "attennato r" on signal
µ:cnerator.
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