[37silverstreak]

Hi Rich,
My thoughts would be it's simply a matter of personal choice. If the device is easily removable and doesn't require circuit changes to work, go ahead and try it! It's not expensive and it is your radio after all.
My personal preference is that I probably would not use one as I don't like the idea of having a solid state device running in my tube radio. Not because it wouldn't work well, but just because it isn't an original type of component.for the sake of keeping things original, but again it is simply a matter of personal choice.
As for using a standby switch, I am not an engineer, but my guess would be it's because seeing as it is solid state and not a tube, when powering it on you would get instantaneous high B+ voltage to the plates of the tubes before the filaments would have time to warm up. This instant high B+ might act like a magnet and pull the coating from the cathode of the higher voltage tubes and damage them. a tube rectifier would gradually increase the B+ and allow the other filaments to warm the cathodes and reduce this effect. But that's just my amateur thoughts, I'm sure there are lots of guys here who are a lot smarter than me who will know the answer.
Whichever way you go, I hope you can enjoy your Philco 38-3xx