The "All American Five"
From the 1930s until the 1960s, electronic manufacturers in the United States adopted superheterodyne radio designs that eliminated the power transformer in order to keep the cost of each unit low.
These radios were nicknamed the "All American Five" because of the manufacturers adoption of a standard complement of five vacuums in that their filament voltages added up to line voltage when in series, which is between 110 and 117 Volts.
The B+ voltage, was derived from rectifying and filtering the line voltage, which amounted to about 160-170 Volts DC (Direct Current).
A tell-tale sign of an "All American Five" style radio, is a lack of power transformer installed on the chassis.
One of the advantages of "All American Five" radios is their ability to run on either a line voltage of AC (Alternating Current) or DC (Direct Current). In some areas of the United States, DC line current was still in use.
A major disadvantage of "All American Five" designs is that it had a metal chassis connected to one side of the power line, which was a dangerous electric shock hazard and required an insulated cabinet and knobs.
Caution, Hot Chassis, Risk of Electrocution!
My Trav-Ler Model 5020, shown below, is an example of an "All American Five" style radio, one wire of the line cord connects directly to the metal chassis when the power switch is in AC mode. This can mean that line voltage potential (110-117 Volts AC) can be on the metal chassis, which can pose an electrocution risk, depending on how the non-polarized AC cord plug is plugged into the socket. You need to be mindful of this when operating "All American Five" style radios with the chassis outside of its cabinet!
The Original Non-Polarized Plug
As mentioned earlier, the line voltage potential (110-117 Volts AC) can be on the metal chassis, which can pose an electrocution risk, depending on how the non-polarized line cord plug is plugged into the power outlet. Below is a picture of the original non-polarized plug connected to the Trav-Ler Model 5020.
Polarized Plug Install
I replaced the plug with a polarized with one that most closely matched the original. The wider blade should connect to the chassis as this is the Neutral connection. The thinner blade connects to Hot. I replace the plugs with a polarized type for all vintage radios of "All American Five" design as it adds a margin of safety when servicing and enjoying the radio.
Performing Safety Check
After the polarized plug is installed, when you plug the "All American Five" radio into an electrical socket, you should detect only a very low voltage (less than one Volt) AC between the ground connection on the wall socket and the metal chassis.
Who Writes This Blog?
John is an IT professional from Cleveland, OH who enjoys amateur radio, ham radio, metal detecting,
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