Sears Roebuck & Co. 1904
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|Manufacturer:||Sears Roebuck & Co. (Silvertone)|
PAGE 7-14 CHANGES
Wells-Gardner 7A Series Chassis
In a few receivers of this model, the tone control condenser C-9, 0.05 mf., 400 volts, has broken down. When this occurs the output plate voltage is applied across the tone control resistor and in many cases the resulting current burns the tone control. For this reason, if it is necessary to replace the condenser or the tone control resistor in this model; connect the side of the condenser which formerly went to ground to the +B end of the output transformer primary, as shown in Fig. 1.
This connects the tone control condenser and resistor across the primary of the output transformer. In this method of connection, should the tone control condenser break down, no damage will be done to the resistor.
Fig. 1. New connections for tone-control circuit of Wells-Gardner 7A chassis
Fig. 2. Resistor values of four-section unit.
In case either the 18,000 or the 20,000 ohm section of the four section armoured wire-wound resistor becomes open, it is unnecessary to replace the entire resistor. A separate 18,000 ohms, 2 watt or 20,000 ohms, 0.5 watt carbon resistor may be used. DO NOT USE THE OLD LUGS OF THE WIRE WOUND RESISTOR TO MOUNT
THE CARBON RESISTORS, AS THE OLD UNIT MAY HAVE AN INTERMITTENTLY OPEN CONNECTION. If one of these two sections, as mentioned, becomes open, it will be best to replace both of them. The values of the four sections of this unit are given in Fig. 2.
Method of mounting and replacing resistors
in Wells-Gardner 7A Series chassis. See Fig. 2.
If the entire four-section unit is replaced, the old mounting holes and the old wiring connections are used. However, if the separate 18,000 and 20,000 ohm carbon resistors are used, they are mounted and connected as shown in Fig. 3. Two single terminal mounting strips can be used for the wiring connections. The leads, which connected to terminals No. 1 and No. 2 on the old unit, are connected to the separate terminals marked No. 1 and No. 2 in the illustration.
P-98002A: 4 Section Resistor (2 wire wound, 2 carbon)
P-D-94183: 18,000 ohm, 2 watt resistor
P-B-94203. 20,000 ohm, 0.5 watt resistor
P-1421: Single terminal Mounting strip
Silvertone 1904, 1906, 1908, 1911, 1914, 1938, 1954, 1964, 1984
Several changes have been made in the chassis used in the above models and they should be noted on the schematic, appearing on Sears page 6-45 of Rider's Volume VI.
The resistor, Rl, has been changed from 30,000 ohms to 40,000 ohms. R3 has been increased from 5000 to 20,000 ohms. R5 has been decreased from 50,000 ohms, 0.5 watt to 25,000 ohms, 1 watt. This last change was made to correct motorboating that was sometimes experienced on the s-w. band "C," due to the 6A7 tube variations.
A tone control circuit has been added. One side of a 0.02-mf. condenser is connected to the lead coming from the grid of the 6F6 to the 200,000 ohm resistor, Rll, and the other side of this condenser is connected to one side of the 500,000 ohm tone control. The variable arm is grounded.
A condenser, 0.1 mf., 500 volts, has been shunted across the 8 mf. condenser, C20.
Metal glass tubes are used in the i-f., a.v.c., and output stages. These tubes are the same types as shown on the schematic in Rider Volume VI.
Note the added model numbers above that should be included in your Volume VI index.
G.E. M-106 Changes
A change is recorded in the GE. M-106 receiver. The type 76 tube originally used as the 2nd detector and
AVC, has been replaced by a type 1-V tube. R-16 in the diagram, originally 1,000,000 ohms, now is 1,100,000 ohms. The GE. M-106 is referred to in Rider's Manual Volume V, as the RCA 262, shown on page 5-105 in the RCA section.
The RAE-68 receiver employs the model 82 Radiola 82 chassis with remote control and the automatic electric phonograph.
Sparton Chassis Similarities
It is possible that some Sparton models may come in for service and that you will not be able to identify the exact chassis because of some suffix letter which may appear in conjunction with the model number. Accordingly, it might be well if you added the following data to your Rider Manual Index:
Models 57-A and 57-B are basically the same as the model 57, shown on page Spartan 5-3, 5-4 and 5-5.
The model 81-A is basically the same as model 81, shown on page Sparton 4-18 in Rider's Manual. V.
The model 105 is basically the 104, shown on page 5-19 and 5-20 in Rider's Manual Volume V.
The values of the tapped resistor strip and the volume control of the Radiola 62 were omitted from the manufacturers schematic. These values are shown in the accompanying illustration. The part number of the tapped resistor is 5810 and that of the volume control is 5811.
Valves of resistor strip and volume control of Radiola 62
The schematic for this receiver will be found on RCA page 1-40 in the revised edition; page *497 in the early edition, and on page 1878 of the Rider-Combination Manual
Philco Model 32
Starting with Run No. 6, the part number of the volume control is changed from 33-5063 to 33-5004, and the wave-band switch from 42-1017 to 42-1123. This makes the design and connection of these parts the same as in Model 89. See Rider's Manual, Volume V, page 5-17.