Marshall Studio 20 Transformer, Mercury Magnetics or Stock 

In my opinion what gives the illusion of more gain (if your not adding gain stages) is adding a 10Henry or more choke. It sounds bigger, punchier, grittier more responsive, and MUCH more aggressive.

I have installed and played numerous Mercury trannies and chokes over many years. I could hear what I expected....meatier tone and a bit more transparent to what the circuit is doing. The output transformers need 30 hours of loud playing to break in. They settle in to a sweeter, fatter tone after that. It is popular for many folks to bad mouth and not want to spend the money. It's a free country, so do as you please...it doesn't mean there isn't a big difference. Perhaps you can't hear it, or just don't care. And, that's cool. I love the improvement. In person, it is quite dramatic, and more colorful in tone. My two cents.

Thank you Dave for doing this. What I meant by stating I was hoping the OT upgrade would make the amp more usable at lower volumes. Plexi amps tend to come into their own with the gain set around 7 as at lower volumes it loses sustain and can sound harsh. Also, I was expecting better string separation and a fuller low end. It achieved the latter, however to my ears the upper midrange change too much, specifically affecting the classic, aggressive Marshall tone. I will install KT66 power amp valves next in my quest,

I heard a considerably big difference! The the Mercury was warmer sounding and beefy and better punch and big bottom end . I also heard a little bit more compression and a little bit looser of a feel . Like a vintage amp should sound. Sa percentage-wise I'd heard about a 25% to 30% difference. I think there worth the money if tone is important to you.

Mercury magnetically transformer is so much cleaner than stock. It’s more a “Plexi” sound than the stock. It’s a minimal difference but I’d try the output transformer and the power transformer change. Thanks for this. I have this exact amp and I have a Bugera power soak that kills the tone a bit. So this could help it a little plus a new power attenuator (an active rather than passive) should help.

I'd really like to hear one with both an OT and choke upgrade. I did this in a DSL100H and it totally "transformed" the amp.

Dave!!! Alabama USA in the work shed with ya!! Did I tell you, Your Band FREAKING ROCKS!!! Are yall on bandcamp?? P.S. 4 years ago you said it was your last Pickup video...... lol. RIP Tyler Hawkins. Your FOO FIGHTERS poster gets me all the time... get that little lump in my throat. \m/(*.*)\m/

Great video Dave. I felt the bigger Mercury OT sounded a bit cleaner, it would have been more helpful for your customer to try and reproduce his problem in your demo (low volume tone loss), also is he a lead or rhythm player? The swapped AC mains in leads were obviously wrongly fitted and needed swapping back. Hope you did?? 😊

I don't think I heard enough change to make it worth the money and time to "upgrade" to one. I'd try a choke in place of the dropping resistor personally. Great video though.

I blew the output transformer on my Hiwatt DR504 head, I had a very difficult time finding a period Partridge replacement not made in China, so I opted for a good Mercury replacement. It gave the amp more bottom end and better mids , great Hendrix type tones. I like the amp more with the Mercury. I stopped looking for a Hylight era Partridge.

I'm listening through headphones, and I couldn't hear any difference. Of course, I'm getting to be an old rocker with hearing loss...LOL. What I have noticed is that on many amps that have received a pair of the red Mercury transformers is that the treble would be a little higher.

I hear thicker mids…more mid compression…

The original transformers are ok quality Mercury tends to be slightly beefier there maybe a very slight difference but it won't be night and day.

Not sure if you could make Big Ben sound decent?

What brand transformer is Marshall using both main and output transformer?? That’s what I would want to know before I voided a 5 year warranty for a $125 output transformer… I know your right definitely can do what you want for sure but I believe I would have tried a nice preamp in front of it with some more Eq a sustainer for more compression a bit more low end and throatier growl punch if you will and if you have another Eq hit the fx loop with delay , reverb pedals then try it if that doesn’t cut it for yeah pickup change didn’t take me long to figure out that I was a Humbucker guy versus single coil Lol . Anyway good luck with your tone search just some things I’ve done and had at my disposal

I prefer the Marshall it sounds tighter and crisper. The Mercury sounds warble to my ears.

Definitely prefer stock

I believe using an applicable choke inside the unit would have given more relevant tone change than changing the output transformers. Transformer changes generally come with hotrodding the amplifier, in order to handle the hotter overall voltages and amperage needs of the audio output. But if your not making those types of changes, its not really necessary. To each there own , of course. The Mercury Magnetics site has plenty of articles and relevant instructions on the reasons to make changes, as well as what you can expect in the way of audible changes.