Mercury Magnetics build the best "tone full" transformers we have ever used --  we use them in each and every custom amplifier that we build.
 
Custom windings, output transformer "voicing", power transformer voltage adjustments, are all "no problem" for Sergio and company.  They even perform rewinds on vintage transformers;  Unwinding each and rewinding it exactly to it's original specifications using the core provided.  You really couldn't ask for a better situation or service.
 
We at Roccaforte Amps have used just about every transformer company out there for prototyping and production.  In doing so, we can't come up with one other company that's willing to work with you  the way that Mercury Magnetics will -- even if you are a small guy.  Paul in sales is friendly and knowledgeable, and he'll help you get the windings you need.
 
Mercury Magnetics is tops and we feel very fortunate to have them as our supplier of custom engineered transformers.  Yet another fine example of a great American Company. 
 
Please visit them at http://www.mercurymagnetics.com