While tube amps are considered the gold standard in the guitar world, they aren’t very efficient.
Anyone who has used a tube amp knows that the technology produces a lot of heat to achieve those rich tones.
But discussion forums have a lot of questions from concerned musicians asking “How hot is too hot?”
Tubes are supposed to get hot and their glass enclosure can reach upwards of 300 degrees Fahrenheit under normal circumstances. To prevent overheating you have to make sure that the amplifier has sufficient ventilation to keep it from baking and that it is biased correctly for its power tubes.
Unfortunately, amp manufacturers aren’t going to pen themselves in by giving you an exact temperature that is beyond normal operating levels.
And although you can measure the outside case of the tubes I’m not sure if that is giving you much useful information.
So let’s focus on what we can do to keep the amp running smoothly.
Is it normal for amp tubes to glow red?
Tube amps famously use a lot of electricity. In order to get the electrons moving inside the vacuum a lot of electrical current has to be applied to the heater component at the bottom of the tube.
So it is healthy for tubes to get hot and have an orange/red glow, especially if you are pushing the amp hard.
For some humor, I don’t remember the exact model of the amp but I think it was a modern solid-state Peavey with preamp tubes that had red LED lights installed in the center of the tube sockets underneath the tubes to make it look like they were glowing red hot. It was sad and funny at the same time.
Now back to business; if you have a class A amp it doesn’t “idle” and will draw power all the time.
Most high-powered amps are class A/B, and the push-pull design heats the tube more in response to how much you are pushing the amp, so check what kind of amp design you have and keep that in mind.
How hot do amp tubes get?
Since the heater of the tube is inaccessible, I don’t think that it is possible to get an accurate measurement of the inside of the tube unless someone designs a nanobot that can survive inside the tube or something.
Somewhere on the internet, someone stated that tube heaters can reach 1000 degrees Fahrenheit but I’m not sure how they got that information so I will just mention it and move on.
Since the glass case of the tube can be measured easily with infrared thermometers, this is about the best we can do.
Some say the exterior of their tubes measures at around 140 degrees Fahrenheit but that doesn’t sound that hot to me.
Luckily someone took the time to document measuring their tubes’ heat with hi-fi tube amps so we can see for ourselves.
So these amps (I think they are Class A) heat the power tubes up to 280-325 degrees Fahrenheit after about half an hour.
And those aren’t even installed inside the chassis so they have the benefit of airflow. Note that the preamp tubes do not run as hot.
For instrument amplifiers, most tubes run on a power supply of 5-6.3 volts but the current (amperage) is highest in 6L6 and EL34 tubes so expect more heat if your amp uses those tubes.
What are the signs of a tube amp overheating?
Your amp is going to get hot not only from the power tubes (there is sometimes a rectifier tube too) but also from the transformer dealing with a lot of current.
And while it’s natural for the heater/filament to glow with heat, the plate in the center of the tube should not be red hot. I have also seen plenty of char marks on tube sockets.
These are your best visual clues but you should listen for poor/weak sound quality, intermittent output, or noises that shouldn’t be there like hisses, squeals, and hums.
Can overheating damage a tube amp?
Severe overheating can cause issues with your tubes, capacitors, and transformers.
And at some point, a combination of heat and vibration could damage the solder joints as well, especially on a single-sided PCB.
If you are certain that your amp is running too hot you should take it to have it serviced before you cook a super expensive component like a transformer.
How can you prevent overheating?
The best thing that you can do is try to move the heat out of the chassis. Some tube amplifiers have internal fans to help with the heat.
But being a mechanical piece of the amplifier, fans are known to fail and are a common repair. If your amp has a fan and it never comes on then have your amp serviced (the part itself isn’t too expensive).
If there is no fan you can usually have the amp modded to use an internal fan but if the amp is under warranty then you will void the warranty.
Another option is to use a clip-on fan with an external battery or power supply.
And of course, you can use any household fan to help circulate air around the amp and dissipate the heat in the chassis (I would keep the amp a little distance from the wall as well so as not to smother it).
I don’t think ambient room temperature is a huge factor but it can’t hurt to at least consider that there can be a thirty-degree difference between a basement and a second-story attic so choose your practice space accordingly in the summer months.
As for the amp itself, a class A/B amp needs to have the bias set when the power tubes are replaced because tubes are always a little different from the factory.
So to make sure that your amp is operating correctly (in the sweet spot) you should have an amp technician do this with every re-tube.
Do tube amps need to warm up?
A tube amp should be ready for output within a minute of turning it on. Really, it doesn’t take long for metal to heat up when you apply an electrical current to it.
Think about how quickly a light bulb filament or toaster element heats up.
And for how heat is too much for an amp, just do what you can and don’t worry too much.
Tube amps are a high-maintenance technology and problems do develop but most of us think that they are worth a few headaches.
Hello there, my name is Ramiro and I’ve been playing guitar for almost 20 years. I’m obsessed with everything gear-related and I thought it might be worth sharing it. From guitars, pedals, amps, and synths to studio gear and production tips, I hope you find what I post here useful, and I’ll try my best to keep it entertaining also.