Restoration of the Stewart-Warner R-113 Shortwave Converter
Author: Edgardo Castro Bruse
San Salvador , August 6 , 2010
Between 1931 and 1934 Stewart-Warner made at least four models of shortwave converters. All of which had the same basic design.
The most important differences were:
a) The kind of tubes used.
b)The way the filaments were fed.
c) The kind of band switch used. The band switch used by the R-113 is by far superior to the one used by the 301-A, and even to the ones used in modern receivers!
It is worth mentioning that the R-113 has its scale calibrated in meters for wavelength, while the 301-A has only a logging scale.
The 301-A is slightly more sensitive, for it has an antenna compensator. But it is a real pleasure to operate the R-113 for it is a single tunning knob unit.
Based on the tube types, band switch, and calibrated tunning scale I have concluded that the R-113 came out after the 301-A.
Repair of the electronic circuit & vernier systemAll original resistors had increased their values too much. To correct this problem I connected in parallel with each resistor the necessary resistance to bring the original resistor to its correct value.
Both 0.02 microfarad paper condensers were replaced by new ones. Below you will find some pictures showing the "before and after restoration" (Click on images to enlarge)
Vernier system restoration
The Stewart Warner R-113 converter uses the same vernier system as the 301-A, and develops the same problems: the rubber cylinders become either petrified or too soft due to weathering.
The top cyliner was fixed by applying several layers of teflon tape. To prevent the cylinder from slippering it was tighten to the shaft by means of a green plastic lace.(Click on images to enlarge)
The bottom cylinder was also too soft and it moved sideways. To prevent this I removed the shaft with the cylinder and put two metal disks at both ends of the rubber cylinder. (Click on images to enlarge).
Now the vernier system was operative and I was ready to deal with the power supply.
Power supply & converter operationThe power supply is built around a small transformer that produces 110 Volts AC and 12.6 Volts at 0.5 Amperes.
The circuit and construction process of the power supply are shown below.(Click on images to enlarge).
The R-113 is connected to its power supply by means of an 8 positions screw-type terminal strip, and a six-wire extension cable.
It must be noted that all original wires of the R-113 are used, and NO modern plastic-covered wires enter the converter or even touch the R-113.
Operation of the R-113
First, connect the output of the R-113 to the antenna input of a BC band receiver by means of a short length of RG-59U (Less than a Meter). Second, with the R-113 OFF, find a clear spot near or at the 1000 KHz. mark in the BC receiver.
Third, turn the R-113 ON by means of the lower knob. This knob operates the mode switch.
The first position of this switch is the ON/OFF. Its second position is the first SW Band (SW1), and its third position is is the second SW Band (SW2).
Now you are ready to operate this gem!
Turn to the SW2. If it is daytime or early evening, search for stations from about the 30 meter mark to the 20 meter mark. Read on the RED SCALE!
If it is night time, search stations from about the 61 meter mark to the 36 meter mark. Read on the RED SCALE!
Band SW1 is only a night time band. Read on the BLACK SCALE!
SW2 tunes from about 4,6 MHz to about 12,4 MHz. Read on the RED SCALE.
SW1 tunes from about 1,55 MHz to about 4,1 MHz. Read on the BLACK SCALE.
Turn the dial knob very slowly and enjoy shortwave listenning 1931 style!!!
I do want to thank my friend German for his professional job at posting this article on line at his web page. Also for his encouragement to continue with my restoration hobbie.
In mid July 2010 I had the pleasure of having Aaron Weed KC2NDA and his fiance at home. My wife and I enjoyed very much their visit, and Aaron enjoyed operating the R-113!
I do want to thank Aaron Weed KC2NDA - who kindly brought me the R-113 from New York - for his willingness to bring me the subject for my next project: A Stewart-Warner 345 TRF Receiver!