[MrFixr55]

Seems from the schematic that te S38 suffers from the same issues that most "AA5s" suffer from, namely the "warm" chassis (Chassis connected to power through a cap or cap / resistor combo, and the fact that the switch is in the "B-, base of heater string junction", making the chassis warm no matter the polarization of the power cord, depending on the position of the power switch. For example, if B- is at "neutral" potential, the chassis will be cold with the power switch on, but "warm" (or hot if the cap shorts) with the switch off, due to the very low resistance of cold tube heaters. If the polarity of the power cord is reversed, then the chassis will be cold with the switch open but warm (or hot) with the switch closed.

I don't know why manufacturers always chose to switch the cold side of the line (They continued this all the way to the demise of the AA5 radio and replacement with solid state devices, including doing this with clock radios). Was it for hum reduction? I don't know, but I modify all of my hot chassis and warm chassis sets to place the switch on the hot side and use a polarized power cord. Of course, I ensure that all safety devices in existence at time of manufacture are in place. However, for example, my Emerson FG330 is a warm chassis set. The chassis screws protrude to the bottom of the cabinet, are metal and at chassis potential. While not common for someone to want to touch the bottom of the radio while plugged in (except the 5 year old version of MrFixr), I see this as a problem.

While installing an isolation transformer is an excellent option for adding safety, adding a polarized plug and putting the switch on the "high side" (rectifier plate and heater), connecting B- and heater low side (usually detector / 1st AF tube to the wide blade of a polarized plug will add safety without much expense. In addition, ensure that all chassis to cabinet isolation is in place and in excellent condition.

IMHO, this should be done on all transformerless sets unless not possible. For example, sets with a "Cordohm" (curtain burner) power cord with the built in filament dropping resistor and many battery / line power portable tube sets are very difficult to perform this mod without replacing the filament dropping resistor portion of the power cord.