I was wondering why Philco has a cover over the transformer on a 40-150 that I am working on? I removed it and find a regular old transformer in nice shape I might add. I was wondering if there was any real reason it is there? I noticed some pictures of this same radio on the internet that show the cover removed and was thinking the thing would run much cooler exposed to the air. I was surprised how small this transformer looks vs other radios I have worked on with a similar number of tubes.
Just a guess, maybe used for extra shielding.
They aren't really stressed all that much, most of the tubes used in the 40-150, 180, etc are 150 ma loctals rather then the usual 300 ma octals everyone else was using at the time, the exceptions being the #41 output tubes and the 84 rectifier, the B+ voltage was on the low side too, only about 180 volts on the power output tubes. Now why did they use that metal box? I don't know, but it obviously didn't hurt anything as most of this series of chassis still have their original power transformers, however the output transformers are usually dead on arrival if they haven't already been replaced.
Regards
Arran
The OP also asked this question on ARF, and someone there speculated that the cover may have been for magnetic/electrostatic shielding.
Sounds reasonable to me, especially given the close proximity of the loop antenna to the transformer. This may be why the console versions didn't have the cover over the transformer - the loop antenna in the consoles was under the chassis, not directly behind it.
But this is another of those questions that can only be fully answered by dead Philco engineers. And dead men tell no tales, nor do they answer any questions.
Yes some interesting replies, seems like it was a fairly common practice with other manufactures of that time as well.