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FatStack™ and Superstack™ Transformers

FatStack™ transformers are custom-designed Mercury Magnetics transformers that have extra steel laminations. In an output transformer this extra iron extends the bass frequency response. In the power transformer it can minimize tone drift giving your amp more stability and headroom.

Our SuperStack™ transformers are similar but are built higher to accommodate smaller mounting footprints.


With lead wires — SuperStack — Uses Grain-Oriented Iron


120V Primary — Drop in Upgrade — SuperStack  — For use in combo amps only – will not fit head version


100 Watt JCM2000 — SuperStack (over 4″ of Iron!) — Drop-in Upgrade!


With lead wires — SuperStack (see FatStack) — Uses Grain-Oriented Iron

Terms of Service

All Mercury Magnetics® products are 100% handmade in California, USA.

Copyright © 1954-2018 by Mercury Magnetics. All Rights Reserved. Mercury Magnetics, Mercury Vintage, Partridge, FatStack, SuperStack, NewVolt, Mini-Choke, Multi-Choke, Mercury Custom Shop, Mercury Boutique, “The Heart & Soul of Your Amp,” “Holy Terror,” “Bad Guitar Tone — Whatever Its Evil Mission It Must Be Stopped!”, “Champ 600 Upgrade,” “XLG Upgrade Kit,” “Mean 13” and “The original British amp tone — shaken, but not stirred,” “Our Transformers are Stacked,” “The Essential Building Blocks of Your Tone,” “Mercury Studio-Pro Upgrade Kit for the VOX AC4tv,” UTM (Universal Transformer Mount), Amp-Saver and Copper-Tone are trademarks licensed to Mercury Magnetics. Axiom, ToneClone, Radiospares, VoodooScrew, Multiple Arrayed Geometric Inductive Coupling (M.A.G.I.C.), and APS (American Pro Series) are registered trademarks licensed to Mercury Magnetics. All other companies, products and trademarks mentioned on this website are trademarks of their respective owners. Unless otherwise noted Mercury Magnetics is not affiliated with any of these companies.

Mercury Mod and Upgrade projects and their documentation are the result of technical investigations made by the engineering staff of Mercury Magnetics. The disclosure of the information herein may pertain to proprietary rights, and the furnishing of these documents does not constitute an expressed or implied license to use such materials.

Mercury Magnetics® transformers and other products are in compliance with the European Union RoHS Directive 2020/95/EC with respect to the following substances: lead (Pb), mercury (Hg), cadmium (Cd), hexavalent chromium (CR (VI)), polybrominated biphenyls (PBB), and polybrominated diphenyl ethers (PBDE).

Mercury Magnetics® founded in Southern California in 1954 and incorporated in 1968.


The voltages in your amplifier can be dangerous. Transformers and chokes are not user serviceable parts. Installation of these components should always be performed by an experienced technician.

The simple ability to use a soldering iron is not enough to qualify a “do it yourself person.” Those who are inexperienced in working with electronic circuits should never attempt to service their amplifier. Household line currents can be deadly!! Transformers, chokes and large filter capacitors can store a dangerous charge for several days or more after the amplifier has been unplugged. Never touch the terminals of such devices without being certain of their charge status. Risk of shock and damage to equipment may result from mishandling and/or improper use of these components. Please use common sense and always think safety first. After all, tone is most enjoyed when you are alive to hear it.


DSL/TSL — Drop-in Upgrade! — SuperStack (see FatStack)


DSL / TSL — use with head ONLY! — SuperStack (see FatStack) — 4, 8 & 16Ω taps — 6L6 / KT66 / 6550 / KT88 tubes — Drop-in Upgrade!


DSL / TSL — Upgrade! — For use in Heads only — will not fit combo version — SuperStack

Add a Real Choke

I’m a player from Los Angeles. Even though I endorse companies like Framus and Brunetti amps, who both make fine equipment, I still rely on Marshalls for some of my favorite tones.

Last month I went on a quest—how can I make my “road-dog” amp, a Marshall JCM DSL 2000, play like my vintage 30+ year old Plexi (which stays home, of course!)?

Well, first I got a tech to change a couple little things: resistors out from the volume pot, a couple of changes with the EQ resistor’s values, etc. This made a bit of difference. Then I played with a variation of power and preamp tubes, from different companies (GT, JJ and Tesla) until I found the combination I liked best. This made a perhaps 25% difference. I was happy, but still searching for that missing ingredient because the Plexi had… well, more of everything, including more power, more clarity, faster response and fuller overall frequency. So, I kept fishing around on the web and by chance hit upon a review for Mercury replacement transformers.

As luck would have it Mercury is located 5 minutes from my home! I thought I had nothing to lose by replacing the transformers since it’s usually a fast and easy tech operation, so I went to see them.

Along with their technical knowledge, what struck me instantly was their level of care and enthusiasm. Mercury’s Sergio Hamernik explained that I could do more than upgrade the existing power and out-put trannies, such as add a real choke to the circuit, like the original Marshalls(the stock DSL has a cheapy resistor instead of a choke).

Although Mercury had something special in mind, I had a gig in a couple of days, so we decided to only replace the output tranny (OT)—then finish the job later. Not all transformers are the same within any model (or year) of amplifier, and in many cases there are radical differences. Mercury makes a particularly outstanding drop-in output that would help the JCM’s sound. Although it was a temporary “patch”this change gave me the chance to feel, let me repeat, f-e-e-l the amp at my gig, and I was positively surprised by the how it reacted and sounded. Simply stated, the improvement with the feel and tone was 50%. After the gig Mercury went to work on my amp by liter-ally re-engineering new power and output transformers specifically for the DSL. The power transformer(PT) utilizes their new “SuperStack” technology (it’s huge and looks like a skyscraper in there!) that completely eliminated the amp’s tendency to overheat! They also modified the circuit by adding a choke. The final result was nothing short of a revelation! The amp has more power, better tone, faster response, wide palette of frequencies… it has more of everything!


View PDF Article


DSL/TSL — Drop-in Upgrade! SuperStack (over 4 inches of iron!)


JCM900 — Drop-in Upgrade! — SuperStack — 4, 8 & 16 Ohm taps –6L6 / KT66 / 6550 / KT88 tubes


100 Watt JCM2000 — SuperStack — Drop-in Upgrade!

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