Sears Roebuck & Co. 1650 Schematic

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Product Information:
Model:1650
Manufacturer:Sears Roebuck & Co. (Silvertone)

Schematics Content:

Please note: this content is a computer-generated interpretation of the above schematic and is provided only to help assist you in locating this schematic. For the actual text, please consult the schematic above. Thank you.

Page 1:

PAGE 6-6 SEARS
mourn 1505
Alignment

OSF/Lum Call

quency stages, no adjustment of the tuning
condenser on the receiver will have any ef-
fect, inasmuch as the intermediate frequency
stage is fixed tuned.

If your test oscillator is properly designed,
it will supply exactly 175 k. c., and when
trimmers number 5, 6 and 7 are set for
maximum output, they will be correctly ad~
justed and should be sealed.

Next, disconnect the 175 k. c._test oscil-
lator and connect to the antenna binding post
of the receiver, the output lead from your
broadcast test oscillator, or tune in a broad-
cast signal around 1400 k. c., then reset
trimmers numbers 2 and 1 respectively for
9 maximum output. This adjustment will track
the super-autodyne grid circuit of the R. F.

To check the callbration of the receiver,
whether it be high or low, trimmer number 3
should be reset until a station of known high
frequency is brought in on the correct dia]
marking with peak volume. If your broad-
cast test oscillator is accurately calibrated, it
might be used in place of the broadcasting
station signal. In this adjustment, a broad-
cast station or test oscillator signal at about
1400 k. c. should be chosen. The setting of
the trimmer at 1400 k. c. is more critical
than it would be at 600 k. c.; calibration.
therefore more accurate.

The next adjustment is important and not

READJUSTING TRIMMERS

Number 1 is the antenna trimmer.

Number 2 is the gang condenser trimmer
tuning the grid of the Super-autodyne.

Number 3 is the gang condenser trimmer
tuning the plate (or oscillator of the super-

autodynel- easily explained in writing, so pay close at-
Numbel' 4 is the Oscillator Padding tention to the following instruction. We

trimmer- will now balance the oscillator to the r. f,
Number 5 is the Super-autodyne plate and first detector sta es. A

trimmer. Tune the external roadcast test oscillator

and the receiver both to 600 k.c., then slowly
increase or decrease the capacity of No. 4
(oscillator padding trimmer), at the same
time and continuously tuning back and forth
across the signal with the receiver tuning
condenser gang. The output meter needle
will now be swinging up and down in step
with the variation in tuning. Watch the peak
of this swinging closely and readjust No. 4
trimmer until the swinging.needle reaches
its highest peak.

Retune the receiver and broadcast test os-
cillator to 1400 k.c. and re-check trimmer No.
3 to make sure that the adjustment of No. 4
has not thrown the receiver out of calibra-
tion. If it has, then readjustV No. 3 until the
calibration is correct, (as previously ex-
plained), and check on trimmers No. 2 and
N o. 1, to make sure that the adjustment of
No. 4 has not reduced the sensitivity.

Number 6 is the I. F. grid trimmer. `
Number 7 is the second detector grid

To readjust the trimmer, it Will be neces-
sary that a good design of 175 k. c. oscillator
be employed, and that a dependable broadcast
test oscillator be on hand so that stages
handling intermediate frequency, and those
handling radio frequency can be thoroughly
checked. It is advisable to use a bakelite
screwdriver when making any of these ad-

First, connect the 175 k. c. oscillator'output
leads from the control grid cap of the super-
autodyne tube to ground. Do not remove'any
of the tubes from the sockets, and it- is not
necessary to disconnect the grid cap clip from
the tube. Reset trimmers numbers 5, 6 and
7 for maximum output. While this test oscil-
lator is working into the intermediate fre~

(C)John F. Rider, Publisher

Page 2:

PAGE 7-6 CHANGES

Changes have been made in the an-
tenna circuit of this receiver, the sche-
matic of which will be found on

Circuit change in Colonial 603

Colonial page 5-19 of Ridefr Volume
V. The new circuit is shown in the
accompanying illustration. The rest of
the wiring remains unchanged.

Colonial 656

In the schanatic diagram of this
circuit, appearing on page 5-37 of Ri-
de/.r Volume V, the third section of the
gang condenser was omitted in the an-
tenna circuit, only the trimmer being
shown. Please draw in on the above-
mentioned schematic a variable conden-
ser shunted across the trimmer, appear-
ing in the extreme upper left-hand
corner of the diagram.

The hxed condenser shunred across
the sooo-ohm resistor in the cathode
circuit of the 75 tube has a value of
0.1 mf. Please mark this in opposite
this condenser.

The value of the resistor connected
betwem the 500,000-ohm receiver in
the grid circuit of the 42 tube and the
junction of the speaker field and the
350-ohm resistor, has been changed
from 4000 to 5000 ohms.

RCA D7-7

In some sets bearing the above model
number, the value of the resistor, R-5,
is 12,000 ohms. This ordinarily is
55,000 ohms. The resistor is con-
nected between the screen grid of the
6K7 i-f, amplifier, and the ungrnunded
side of the 10-mf. condenser, C-ZZ.

The usual value of the resistor, R-19,
which is connected between the grounded
heater terminal of the 6A8 tube and
the same tube's oscillator grid, is 100,-
000 ohms. In some sets the value of

Sometimes heterodyning may be en-
countered on these sets due to excessive
antenna capacitance. This may be cor-
rected by reducing the size of the an-
tenna or by inserting a ISO-mmf. con-
denser in series with the antenna leadA
This may be done in the receiver by

removing the brown lead which goes
from the antenna terminal to the wave
trap inducrance, L-l, and inserting the
condenser between these two points. In
some instances, interference in the form
of "beats" may be remedied by tuning
the antenna wave trap to that station.
The wave trap will tune up to 700 kc.

The selectivity of this set can be im-
proved by disconnecting the two leads
to the small choke coil in the lst i-f.
circui't and inserting in its stead a 0.005-
mf. fixed condenser. ('lhis choke coil
is in parallel with the 20,000-ohm re-

1? rem-nat some

Subsiilufing e condenser for *he choke
a Modal |650.
sistor in the input circuit of the 58 i-f.
tube. See Rier Volume VI, Serarr
page 6-7.) After this substitution, the
i-fA stages must be re-aligned with an
oscillator. This re-balancing is very
important, as the :Eect of the change
will be lost if it is not clone. See ac-
companying sketch for locations of coil
to be removed and condenser to be sub-

Reception can be often improved by
the insertion of a choke (Part No. R-
8501) in the red plate lead of the 285
rectifier. This will reduce the hiss or
feedback. In some instances this tube
may cause interference within the set, as
well as other sets in the vicinity. If the
use of one choke does not eliminate the
trouble, a similar choke can be inserted

How theater. a, imma in n.. sms.
Roebuck IMO for reducing hiss.

in the other plate lead of the 285. See
accompanying illustration for installa-
tion of this choke. For schematic dia-

gram, see Rider; Volume III, Sears page
3-12 and page 2098 in Rider-Combina-

The undesirable eliecr of time lag
_(weak programs interrupted during
bursts of static) can be greatly reduced
by replacing the 0.1-mfA condenser, con-
nected between the plate and cathode
leads in the type 57 AVC tube, with one
having a value of 0.01 mf. Making this
change minimizs the time lag dimculry
when tuning in distant stations in some
localities without affecting the AVC
action. The reduction of capacity lessens
the charging time of the condenser and
therefore the AVC recovery is practi-

The schematic diagram of this Sears-
Roebuck receiver, appearing on page
5-45 of Rider; Volume V, should be
changed according to the manufacturer.

There should be no choke coil across
the upper 0.5-mf. condenser in the
vibrator circuit.

The on-oli switch should be in the
other 32-volt linHQt in the same line
with the 2.5-amp. fuse.

The tap in the primary winding of
the power transformer should go to the
52-volt line ro the right of the on-oH
switch` In other words, the 0.5-mf.
condenser should be across the 32-volt

The secondary of the power trans-
former should be tapped and connected
to the junction of the two 0.5-mf. con-
denser; that are shunted by the Globat

In some receivers carrying these model
numbers a felt ring between the small
speaker and the baliie was omitted, with
a rattling of the speaker resulting. This
is due to the fact that when the mount-
ing screws of the speaker draw the
speaker tightly against the baEe, the
speaker frame may become slightly bent,
throwing the cone oE center. The felt
ring acts as a cushion mounting to pre-
vent this bending. Do not tighten the
mounting screws any more than is neces-
sary. If this felt ring is missing, one
should be inserted, 'its part number be-

The volume control used in this re-
ceiver is rated at 5,000 ohms. The
schematic wiring diagram appears in
the Rider Combination on page 915
and on page 1-15 in the Fada section
and also on page *79 in the early edi-
tions of Rider's Volume I.

(C)John F. Rider, Publisher

Page 3:

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Page 4:

PAGE 6-8 SEARS

MODEL 1650
Voltage
Transformer Date.

58 e Translator 100

22'! - let LF. 95 1.5

Hag Current
50 La. eech plate

241 _ output 215 :zo e

280 - Rectifier hx. 4.8. volts g 415 volte

# High eerie. resistance.

Control grid readings taken on 150 volt ecale ot 1000 ol-e per volt
when other. on 'ISO volt scale. Become the A336. action would change
voltages and currents, no lignal should be received when readings are
taken. These are average valuee, Usually, deviations up to 2M are
pemesehle and do not necessarily indicate a fault. 'here eeriee grid
resistors prevent grid voltege reading, proper plate current et rated
plate voltage will nerve ae an indication ot proper grid bias and moral
functioning ct the tube. Cara mt be ueed when readinge are baba vith
an analyzer since the capacity of the cable my eau" the circuit to
oscillate and give erratic readings. Ulmlly, touching a finger to the
grid or plate 'ill stop oicillaticn. I

PGYER TRANSFORWR COLOR CODE

REC TIFIER PLATE

PRIMARY

Red; Blue. Slate center tap-

Strended wire leads.

Green; Black. Stranded wire leads.

REC TIFIER FILAMENT

Solid wire leads.

Red. Solid wire leads.

Solid wire leads.

(C)J?hn F. Rider, Publisher

Page 5:

Trimmers

SEARS PAGE 6-9
Transformer Date.

gamma aiodvo

ELK

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@John F. Rider, Publisher

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