Ask the Amp Man -- Jeff Bober

Q: I have a 1993 Fender Blues Deluxe reissue and I love the tone but want just a little more clean headroom -- maybe 50-60 watts instead of the 40 watts that the amp is rated at. I was wondering if it is possible to change the output transformer on this amp to give me an extra 10 watts or so? -- Michael Cadó

A: Good question! The succinct answer is no, but there actually may be some benefit. Let me explain.

The output power of a tube amplifier is not totally determined by the output transformer, but also by the power, or mains transformer, and the voltage and current it supplies to the output tubes. The job of the output transformer is to take the power developed by the output tubes and convert it to a form that is usable by the speaker. The problem with replacing just the output transformer with a larger one is that there is simply no more power available from the power transformers and tubes to convert to more output.

However, occasionally there is a perceived increase in output when a larger output transformer is installed in an amplifier. To substantiate this, I contacted my friends Paul and Sergio at Mercury Magnetics, manufacturers of some very cool iron. Here's what they had to say:

"By starting with the right transformer, or upgrading an inferior transformer, a player can get more out of the amp and experience extended clean-tone headroom and a noticeable presence of a bigger sound stage effect. Increasing an output transformer's frequency and tonal capacity with more of the right kind of iron and copper will result in more inductance to the primary winding. It's this inductance that has a profound effects on the tone and how large it sounds."

In plain English, a larger and better quality output transformer will generally make an amp sound bigger, without actually having any additional output power. This is especially true with amplifiers that have output transformers designed to be just big enough to get the job done -- a design theory that, I might add, is pretty foreign to us here at Budda. We believe in the concept of "bigger is better" and "size does matter." (Ha, ha.)

The bottom line is you could have the output transformer in your Deluxe replaced with a larger capacity output transformer such as its big brother the Deville, or an even better upgrade transformers from Mercury, and hope that it achieves the results you desire. This modification, however, is not for the inexperienced as the PC board needs to be lifted and additional mounting holes drilled. Of course, you could go all the way and have the mains transformer replace with a Deville or upgraded transformer as well. This again is not for the inexperienced as the chassis cutout needs to be enlarged -- but according to the original '93-'94 schematics, the circuits are virtually identical, so you could have yourself a 60-watt amp in a 40-watt body, except for the 50-watt speaker.

Good luck, and have fun crusin' with your new Deluxe Deville.


Source: Premier Guitar

Edition: October 2007

Article: Ask Amp Man with Jeff Bober

Trace Davis is the president of Voodoo Amplification Inc., which is considered to be the world’s leading modification company and one of the foremost experts on vintage Marshall amplifiers. Trace is also an experienced session player, touring player, recording engineer and producer.

Jeff Bober, co-founder and senior design engineer for Budda Amplification -- www.Budda.com
Email Jeff at: jeffb@budda.com

Copyright
© 2007 by Jeff Bober.