Benefit of Using Mercury Magnetics Transformers

OK, so perhaps you’re sold on snatching a stock Pro Junior, but of course, you want it to sound the best it possibly can…. Should you wish to dig a little deeper in the quest for tone, veteran amp builder Ben Fargen has developed a line of Hot Mods for stock production amplifiers – lots of them, including the Pro Junior, and we asked him to describe the inspirational behind his concept for the Hot Mods….

“For a number of years I had a lot of people wanting me to work on their vintage Fender, Marshall and Vox amps, and I really never had the time until the economy slowed down in 2008. A local customer asked me to take a look at a Marshall JCM800, which (laughing) really isn’t the kind of amp I’d usually be interested in, but I agreed to look at it, got in touch with Mercury Magnetics, went through the schematic, and wound up turning it into a really great sounding high-gain amp that would appeal to people who like that sound. I had also done some design work for Carvin when they wanted to optimize a production design and get the most out of it, so when the economy slowed down I began taking in specific camps to upgrade, and from there we started developing mod kits. Customers went just their chassis in, which isn’t expensive to ship; we do the work and ship it back.

Through the later part of last year we were doing about one mod project a day, at first taking in just about anything, but we’ve since whittled it down to specific amps like the Pro Junior, Blues Junior, Blues Deville and the reissue blackface Deluxe Reverb, for example. With these amps it’s not the design that’s the problem – it’s just that the component selection is based on what is most practical and economical for an affordable production amp. We take those amps and optimize the sound as if production cost was not an issue, and we have customers who have had two or three different amps modded now, because they are basically getting a boutique amp and the tone that comes with it.

TQR: In the Pro Junior specifically, what areas of the circuit do you focus on for the mods?

There are really only so many ways to wire up a tube amp circuit, and in most cases we’re focusing on the same key areas in each amp – plate resistors, coupling caps in the EQ and phase inverter, and slop resistor for the EQ, and cathode resistors and cathode bypass caps are huge and often overlooked…. We hone in on the tone-shaping improvements that give us the biggest bang for the buck, and of course the Mercury transformers make a big impact. You can do any of these mods alone and improve the sound, but it’s really the cumulative benefit of using specific high quality components and the Mercury Magnetics transformers that determine the end result where you really hear the magic. We aren’t the only people doing mod kits, but you’ll notice that we use specific brands and types of caps and resistors in very specific places with our mods, and that’s the result of my having build amps for 12 years and learning what specific types of components are going to do in a particular part of the circuit.

TQR: You also added a power supply choke in the Pro Junior you modded for us….

We add the choke because it is so critical to what I call pick dynamics – the note response to pick attack, and improved sustain. Most budget amps just have a power resistor separating the B+ and the screen voltage – it works and does the job, but the correct choke in a circuit really adds a huge amount of that ying and yang you want to hear between the power amp and the preamp.

TQR: And what is the cost of the Pro Junior mod as you’ve done this amp?

With the full Mercury transformer set it’s $499 without a speaker swap. All the Hot Mods are in the $349 to $549 range until you get into 100 watt or JTM45 Marshall reissues and things like that. We’ve also done a lot of mods for the reissue Bassman…. As you know, there is nothing like a great Bassman, and there are a few revisions that Fender made that are just not happening at all, but when you get rid of those they can sound fantastic.

Here’s the deal…. You economically ship your chassis per Fargen’s instructions and they ship it back fully optimized. We asked Ben to send us a Hot Modded current production Pro Jr. for review and we directly compared it to our stock 2001 Junior, fully loaded with our NOS tubes and Jensen Vibranto. The modded amp Ben sent included stock Groove Tubes and a new Celestion Greenbackten.

As soon as we played through the Hot Modded amp, we heard the same dominate midrange push and lack of treble presence we had heard at first in our own amp. Less pronounced with brighter single coils, yes, but still too middy for our taste, so we subbed in the JensenC10Qfor the Greenback and the angels were singing again – sopranos, altos, tenors, and baritones all present I the choir. In fact, both amps sounded similar with the stock tubes in the Hot Mod Pro and our stock model with the NOS tubes – thick, rich and very smooth with excellent dynamic response and full, clear fidelity. Fargen’s Hot Modded Pro Junior possesses smoother, warmer overall tone while our Pro still sounds brighter and a little glassier overall. We suspect that a bias pot and lower voltages would tame the intensity of the distortion, but the 5751 does a nice job as an easy workaround. Fargen’s amp was also a little quieter at idle than ours, although we hadn’t noticed this until we had a quieter amp for comparison. For more information on all of Fargen’s modifications, check out the Hot Mod pages on the web site.


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