Caption: Photo shows measuring the temperature of a transformer’s laminations with a NON-CONTACT thermometer. In this shot the transformer is outside of an amp and hooked up to a Variac. This type of handheld thermometer does not require direct contact with the transformer and can read temperatures from a safe distance.
Transformers designed with high-temperature insulation systems can run safely at temps up to 200°F. But remember, a hot-running transformer is an angry transformer.
Want to know the health of your amp’s transformers? Take their temperatures! A hot-running transformer is an angry transformer and it may very well be telling you its dying. It could be an older vintage unit that is showing signs of aging materials. Or, you may have a newer amp with a far-to-common undersized “runt” transformer. Either way heat means a waste of power and potentially shorter transformer lifespan — not to mention strangulation of your tone. Transformers should normally run between warm to very warm temperatures. Hot is a bad sign — especially in the case of output transformers (OTs). Make sure that other components are not the cause of excessive transformer heat. For example the tubes should be the only hot-running component in your amp. But keep in mind that if they’re too close to a transformer they could artificially heat the unit, also leading to damage over time. Of course there’s more to the story, but if you are in doubt then see your local amp tech or give us call. By the way, Mercury recommends using a non-contact thermometer to take your readings. If you do have a dying transformer it’s time to think about a rebuild, replacement or upgrade. Remember, Mercury offers you not only the best-sounding and most reliable transformers, but more tonal choices than any other company!
Did you know that hot-running transformers not only drain your amp’s reliability but can also cause major tonal issues?
The problem is so common that many players mistakenly assume that transformers should run hot. Not so. In fact, excessive heat is an all-to-common sign of under-powered “runt” transformers that are potential tone-killing accidents waiting to happen.
Heat is nothing more than a symptom of energy loss. And hot-running transformers certainly do nothing to contribute to your tonal quality. Energy loss means one thing—inefficiency. It’s like driving a hot rod around with the parking brake on. Think of “runt” transformers like brakes on your amp, making your tone dark and muddy.
Here’s why: Insulation aging is accelerated by higher temperatures. As insulation temperature approaches redline, resistance begins to decrease. A breakdown occurs when insulation becomes damaged by the unchecked rising heat. Transformers wear-out from the effects of usage, time and high temperatures.
Exposure to electrical spikes can also contribute to stress on the transformer’s insulation system. If that wasn’t enough, the coils of wire inside your transformer are often beaten up by vibration! These internal vibrations sometimes cause the magnet wires to rub against each other, wearing off the insulation and causing short circuits.
The life expectancy, and resulting tone, of a transformer is completely dependent upon its insulation system. The build-quality and consistency of the transformer design must be greater than the working conditions and stresses you subject it to (i.e. how hard and often you play). This explains yet another reason why transformers wound with paper tube bobbins are the most susceptible to thermal- and aging-related breakdowns.
Remember, a hot-running transformer is an angry transformer. It is angry because it is overstressed. This may not cause your amp to immediately fail, but eventually it will. The ideal transformer should run between cool to very warm. Excessive heat is nothing more than the amp’s circuit demanding more power than it’s transformer can give. The proof is when you correct the problem. Swapping the “runts” with higher-efficiency upgrade trannys gives you enhanced tone by way of increased headroom, higher loaded voltages, better response and often a very perceivable tonal depth improvement.
Getting you both superior transformer tone and reliability isn’t easy. At Mercury we tackle the problem by making uniquely musical transformers for specific guitar amp designs. Each transformer is made by hand, one-at-a-time, then individually hand-tuned for maximum tonal performance — and coolest running temperatures. No other approach comes even close.
With Mercury transformers you’ll have one less thing to worry about in your quest for great and consistent guitar amp tone.
Source: https://mercurymagnetics.com/pages/_misc/FAQ.htm#Take_Your_Transformers_Temperature,%20Part%20I
