Novels can be written on transformers, how they are designed, what materials can be used, how those materials effect tone, etc. (I'll try to put this in context that is easy to follow or understand verses explaining it from an overly technical point of view, which often times only serves to confuse the issue.)
If you installed a 4 cylinder Ford or GM engine into a Ferrari it would be safe to say that the Ferrari would not perform or handle like a Ferrari should, even though the potential is clearly present on the rest of the car. It would look the same but to say the least the performance would be greatly altered. To take this one step further; If you had 10 different output transformers made to the exact same specs but the laminations were made from metal from 10 different countries, you would have 10 very different sounding output transformers. This is just one aspect and there are many others (IE: winding styles/methods, bobbin used, thickness of the wire, what the wire is made of, insulation material used, etc.)
Here are few common questions that we are asked when someone is thinking about replacing a transformer(s) in their amp;
"How much is the tone altered and on what scale can we gauge this?" How much the tone is altered may or may not be obvious and this greatly depends on the experience and skills of each individual player. It would be more obvious to an experienced player, IE: someone who has been playing for years. It may not be as obvious to someone who is fairly new to playing or has not been playing all that long.
"Do all amps need to have the transformers Upgraded?" No, naturally not all amps require new transformers. If you are not certain whether or not your amp would benefit from a transformer upgrade then we would recommend consulting with an professional tech who has built, designed and/or Modified amps for years.
"Will a new output transformer be the magical cure?" No, seldom is it the magical key that cures everything you dislike about a given amp. It can certainly make a profound difference but it will not change things such as Gain structure, an overly bright amp, an amp that has too much bottom end and so on. Those are things that need to be addressed within the amps circuitry as often times it is inherent to the way the circuit/amp was designed, which can be changed.
Having said all that, let me say this: I think if you go with a well-made output transformer and you have an ear for tone then you will not only hear the difference but you will also feel the difference in how the amp handles and performs. Naturally it all comes down to tone and how finely tuned each player's ears are.
Q & A with Trace Davis & Sergio Hamernik
"Does the power transformer have an effect on my amplifier’s tone?" Answer: Yes it does. It is the link between the power company’s energy supply and the energy needs of your amplifier’s circuit. Wimpy sounding amps usually have wimpy power transformers in them. The delivery of energy from the power company to your amp is largely determined by the power transformer’s size, materials and build quality. This affects how much and how fast this energy is supplied to your amp. Does your amp sound like it coughs out each note? Do over-driven chords sound muddy or mushy? Does your amp sound small or dark? If the answer to any of these questions is yes, then you might want to take a closer look at your power transformer and see if it needs an upgrade.
"Can Upgrading to a Mercury power transformer and choke actually lower the noise floor of an amp?" Answer: The noise floor of your amp or any noise affecting your amp can come from a bunch of things. Worn out tubes especially rectifier tubes will make your amp noisier. Filter caps drying out over time will also contribute to increasing noise. Ground loops from poor amp design or build quality are another example. A good power transformer will go a long way to filter out or block noise from your AC line. If it’s designed properly, it should operate with a low magnetic field to minimize the potential of hum being picked up by the audio circuit from the power transformer. The choke if it’s sized right will do an amazing job of cleaning up and smoothing out diode noise and ripple on the DC voltage to the tubes. Clean DC means lower noise.
"It seems to be common knowledge that cheaper Output transformers seem to short easily compared to a Mercury, why is that?" Answer: A transformer is basically made up of copper wire, metal core material and an insulation system. Add to that the labor/time to put it all together. Making a cheaper transformer fit a low budget forces compromises on all these points. All of which adds stress to the transformer by pushing it harder. Nothing clever here, charge the customer less by giving them less. A smaller transformer, less copper, less insulation, cruddy core material and spend less time building it. The end result is the transformer runs hotter and is less reliable. Tone suffers a great deal as well. Nothing will dull out tone faster than a low budget transformer.
"Aside from a choke better regulating the power supply, how else does a choke impact the tone?" Answer: Unlike passive components such as filter caps and resistors, a choke behaves more dynamically in the power supply circuit. It is connected in series, meaning all the B+ energy has to go through it before it gets to the audio circuit. Not so with filter caps. A choke has a natural tendency to oppose changes in current. Not so with resistors. How does this impact tone and how does the guitar player perceives the performance of the amp with a proper choke in place? Typically a noticeable immediate and seamless response time from the amp to the player. Guitarists who record for a living report back that their amp seems to be playing them back with an increased intuition and better note separation. A stronger bond between player and amp is formed when the amp becomes more responsive. Did you also know that early amp designers discovered an increase in tube rectifier life expectancy with the use of chokes? The same holds true for power transformers.
"Do the metals make a difference in how a transformer sounds or feels?" Answer: By metals, I assume you are referring to the transformer core material. If so, then the answer is a definite yes. The core material acts as a magnetic field amplifier between the primary and secondary coils and the character of its composition does impart on to transformer’s performance. The core is made up of an iron alloy and once again it boils down to time and material. The recipe of the material and the time it takes to process it makes all the difference to the sound and feel of your amp.