# Sears Roebuck & Co. 1650 Schematic

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Price: 8.00 In stock  Model: 1650 Manufacturer: Sears Roebuck & Co. (Silvertone) ## Schematic Pages ## 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: .Bo com #d on! nova .5 no :organs alum .Duggan usd."vo
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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
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-

REC TIFIER FILAMENT

(C)J?hn F. Rider, Publisher

#### Page 5:

Trimmers

SEARS PAGE 6-9
Transformer Date.

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ELK

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@John F. Rider, Publisher

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