Transformers PT vs OT

[Ed_Chambley]

I am wondering if there is a need for high end (Mercury Magnetic) Power Transformer.  I have never used one of their PT's because I do not know if they have any influence on the tone of an amp.  I normally just use a Hammond or one of Hoffmans in a PT.  Now in a Output Transformer, I have tested different ones in the same am.  I did it on my current 5f4 build and ended up using a MM Output Transformer designed for the Supro T-bolt.  It really sounds great.

My question is could some of you guys who have a better understanding explain if there is a need for an exceptional power transformer other than durability.  Can they add to making a better sounding amp? 

[FYL]

MercMag xformers are really nice, but IMO vastly overpriced if bought retail. Some of their OTs are quite unique and give better results than standard models. Their PTs aren't better than other quality models from other brands.

[Tone Junkie]

From the 2 PT,s from Mercury Mag. I have used they sag more that others which tells me there not built as well, on a blues amp they work fine if thats what your after but I dont like that much sag and can get all I need from from a tube rectifier circuit, maybe Im just bias because they cost to much.
 I would much rather have a heybor, magnetic components or a hammond over there,s anyday.
That being said they do make some unique OT,s like the last poster said, but others make great over specked OT,s for much less money.
Just my 2 cents
Thanks Bill

[FYL]

From the 2 PT,s from Mercury Mag. I have used they sag more that others which tells me there not built as well

High source Z is part of the design : MercMag tries to replicate vintage PTs which showed the same characteristics.