What’s the deal with brands of Transformers?
If you are into amps you probably have heard lots of hype about different transformers. There always seems to be that person who replaced their transformers and claim that they suddenly had a magical sound. Sounds too good to be true…but is it?
In my opinion different transformers do differ in sound but if they are wound to the same specs the differences in tone are very minor. However many cheaper transformers sound less toneful because they are simply wound differently with cheaper materials. So which ones are best? To really understand what going on let’s go over the types of transformers and their function. By knowing this we can separate the hype from the truth.
The four types of Transformers:
Power transformers provide power to the amp. Basically the power transformer plugs into the wall voltage and turns that into the voltage your amp needs. The power transformer is not in the signal path so it does not directly affect the sound. Two power transformers from different companies that have the same specs operate exactly the same and sound exactly the same! The only consideration is reliability. A really well built transformer will of course last longer but it will sound no different.
There are many companies that cheap out on the power transformers in lower end models---the transformers are poorly made or under spec'ed. The Fender Blues Junior is good example of one of these. They also cause additional sag since they cannot keep up with current draw of the power tubes at high volumes which can make the low end of the amp mushy. They also in greater danger of blowing. You do not want to skimp on a power transformer!
Some amps use a small transformer inductive device called a choke. It not transformer but looks like one. A choke basically smooths out the power supply ripple . Again these do not affect sound if the chokes are rated the same! You want quality materials here but it is not in the signal path.
In amps that have a tube reverb have a reverb transformer or driver. This transformer’s job is deliver the signal to the reverb tank. Since signal passes through it you want a high quality transformer here!
This is the really important one! The output transformer basically transfers signal from the power tubes to your speaker. This is the most critical transformer in any amp and really makes a difference! Your whole sound passes through it. There are different methods of construction and winding styles that affect the sound.
An important thing to keep in mind is that different transformers are wound differently. Typically guitar amps have either straight winds or inter-leavened winds. Straight winding is cheaper to manufacture and sounds different. It not necessarily good or bad but different. For example many Tweed Fenders use inter-leavened wound ouputs while Blackface Fenders often used straight winds.
Some folks will judge an amp by the size of the output transformer but this is matter of taste. Some designs sound better with a small output transformer. Generally speaking the larger the output transformer the more low end and clean headroom (in the power stage) the amp will have.
Importantly output transformers have different primary impedances. Tubes are fairly flexible so the specs on transformers can be too. Fro example a Deluxe Reverb uses a 6.6K primary impedance while a 5E3 Tweed Deluxe has a 8K. These two winding sound slightly different. An experienced designer selects the impedance carefully for the sound they want.
So what about brands?
There are a few different brands with the best know ones being Weber, Heyboer, Classic Tone, Hammond and Mercury Magnetics.
Weber transformers are made overseas and are cheaper than the other brands. They actually sound good to my ears. They are built reasonable well, there is wide selection and have useful features. I have had few power transformers fail over the years so I am careful to make sure the model I use is over spec'ed for the amp if I use one. I use these occasionally in my amps they work very nicely as long as they are used conservatively. That said I think that the USA made output and reverb driver transformers do sound a bit clearer and punchier.
I have used lot of Heybeor Transformers and they are nice American made transformers. Some use modern plastic bobbins and some use paper bobbins. They sound great! Trainwreck and Dr. Z Amps use Heyboers as do many other high end builders. They are priced about the same as Classic Tone Transformers and I use them interchangeably. Since Heyboer never directly retails transformers you usually get them through a supplier. Weber and Mojotone both carry them.
These Transformers are made in Canada and are of high quality. Hammond uses plastic bobbins on their modern transformers but use paper on many of their reproduction transformers. I would not hesitate to purchase an amp with Hammond Transformers. I have used them in my amps and find them to be very nice and extremely well built. The power transformers are especially useful with their high filament current ratings allowing for more tube swapping possibilities. They are bit rarer to find on US made amps largely because the prices tend be bit higher in the US.
Classic Tone Transformers:
I often use Classic Tones in my builds. They sound really good and are built very well. What I like the most about them is that they are made with paper bobbins like vintage transformers. It gives them a rich sound vintage sound. They are a good value for the price. Classic Tone's sister company Marvel Electric produces transformers for various online suppliers as well. These are high quality units too and the same as their Classic Tone brethren.
These are the one people talk about. They are great transformers but function and sound no better than Classic Tones, Heyboers or Hammonds. They also use more modern plastic bobbins so don't sound to my ear quite like the original transformers they mimic but this is only a very minor difference . At 3 to 5 times the price (largely because of all the advertising) it’s hard to justify using them. I personally dislike the advertising they use and mod kits they sell because they are misleading. The amp world is full of misinformation and I do my best not to support it. I only use Mercury Magnetics upon request or to replace a difficult to find transformer because Mercury has a really wide selection of odd ball vintage replacements that few others have. Some people believe they just have to have them but I'm not convinced there is a significant difference.
There are other transformer makers. My rule of thumb is that US made brands are generally pretty good but oversea transformers are better avoided.
If you judge an amp simply by the brand of transformers in it you are doing yourself a disservice. Transformers are important to sound but not because of the brand but because of the choice of transformers in relation to the circuit design. Transformers are simple devices and many companies make quality transformers. Quality is important but hype is only a shelter for the under-educated or under experienced.
An amp designer the proper knowledge and experience will not rely on brand names and hype. A good amp designer can make great amp with many different brands of transformers since they will use judicious transformer selection (specs, size, etc.) and have the ability to tweak the circuit to sound it's best. No matter what brand of transformers an amp has a poorly design circuit will sound bad.
If you are considering changing transformers as an upgrade you should consult the schematic and know why or if the upgrade is going to achieve your goals. If you cannot properly access that question then ask for help from an expert. Do not rely on the sample size of one experiments on internet forums for enlightenment or adverts from transformer companies. There are cases where changing transformer makes sense and some that do not.