Originally Posted by
Joseph Smith Jr
One simply has covers, or bells, the other does not
They are, or can be, functionally identical, meaning the values found at the taps
The windings and subsequent taps determine the transformer's ratings, the bells have nothing to do with it
Leaving off the covers simply saves a few pennies per unit
End bells can conceivavbly offer some degree of shielding if a unit is used in a sensitive area, but the efficacy of such would be circuit and design specific
Many times, transformers with bells are also potted
There may, or may not, be any technical difference between these two SPECIFIC examples, only a service manual or actual measurements could tell me this for sure
But the bottom line is, it is merely a difference in manufacturing execution, not functionality
It is also to some degree a cosmetic and safety practice
The covers have noting to do with the function of a transformer, other than to facilitate potting and theoretically make for a safer and more quiet unit
In the case of these two amps you have presented, the difference is probably because JBL sourced them from different vendors, or, the vendor changed their design
One of them could even be an in the field service replacement, I do not have enough intimate knowledge of these amps to tell you whether or not that is the case, but I doubt that it is
You can see quite clearly that more than a few parts underwent changes either in design or supplier over the life's run of the model
No, you don't need to worry about changing your transformer
Joe