Why Does My Guitar Tube Amp Lose Volume?


You might have been practicing some heavy riffs on your tube amp. But what happens when your tube amp loses volume a day before your next gig?

I think your amp might be trying to tell you something.

But relax, I’ll talk you through it. If you’ve never had this problem before there’s no need to go looking for a new amp. I can help you solve this problem quickly and walk you through all the ways to find out what’s wrong.

It might be your first time dealing with this situation, so there’s no cause to panic. I’ve had years of lessons learned before I started to fix my amp problems before they start. In fact, here’s why I’m going to tell you how a simple volume problem is fixed and how to keep it from happening again. You won’t need to take it to a repair shop after you hear what I have to say. And after that, you can use that money saved on easy repairs and use it for scoring some new FX pedals instead.

Every problem has a solution

Luckily, amps aren’t rocket science even though a tube amp looking like something NASA designed back in the day.

That first day you plugged it in and it was roaring at full-blast just at 3 or 4 on the main volume. And now you’re sweating bullets before the big show asking why does my tube amp lose volume? My first instinct tells me that it’s going to be the tubes. If it’s not one of them, it’ll be half of them; or just a couple select tubes. Let me tell you how it works.

And here’s how to fix it yourself

As soon as you start to hear the sound is dropping-out, you need to turn off and unplug your amp. Let it sit for like 10 minutes, so all the juice is out of the wires.

If you heard crackling-popping sounds, feedback, or microphonic’ sounds, that’s a sign that some tube is bad.

Take off the back cover of your amp and you’ll see the tubes easier. Use a penlight to inspect all of the power and preamp tubes. You’ll need to remove all the tube sleeves if they have them. The inner housing is a flat silver-grey.

This is called the Getter’ and it’s a special coating. If you see rusty-red plating spots on that grey surface, that tube is bad.

The next part is the pencil test. Go ahead and plug in the amp, but take out all the jacks and FX loops first. You don’t want anything plugged into it for this test. Carefully inspect the tubes to see them lighting up. I bet you the one that has the reddish plating on the grey getter is lighting-up like Christmas. That tells you it’s bad and needs to be changed.

So then you need to do a final check with a pencil. Use the wooden part to tap each of the preamp tubes and main power tubes. A good tube will be a dead ‘thud’ sound, so if you hear one that has a high ringing rattling sound, that’s the bad tube.

Bad tubes will make volume drop and tone sounds will be dulled. When a tube goes bad, this is exactly what happens. Turn off your amp (like before) and after 10 minutes you can wiggle and pull down the tube.

Learn to be an amplifier detective

Are there other ways to find out if a tube amp loses volume? It all depends on the color of the tube on the inside. Even if there’s no reddish plating on the tubes’ silver-grey getter, the glowing color of a tube tells you what’s going on inside it. Here’s how you can check the tube glow.

Orange

This is the best color that tells you the tube is working just fine. If this color starts to go red, this means it’s starting to go bad. There will be red glowing spots on the sides of the Getter that are burned-through with reddish bleed coming through. It needs changing at that point. Red can also mean it can be a possible fire hazard from all that heat your tube is making.

Blue

It’s not uncommon that a healthy tube looks blue. Gasses inside that little tubes’ vacuum can be bright neon blue at times. It’s a totally normal side effect that can happen.

Pink

This is normal as well but is caused by too much gas inside the vacuum tube that makes the light appear pink. If your grid amp current is working overtime, this can be spotted inside the tubes too.

Purple

This is a faulty tube that has an air leak. It looks like some cloudy purple haze from gasses that are mixing with outside ions in the air. If you see this, your tube needs to be changed real-quick! It can be a fire danger from the heat its making and cause damage to your amp too!

Other ways to check your tubes

Your amp will have main power tubes and preamp tubes. There are also reverb tubes when your amp has built-in FX settings. Wherever the volume drop is coming from it’s going to be from one of these as well. There’s an order to how this works but it’s not hard to see why.

Power tube

If just one power tubes need to be replaced, you have to do it in pairs. This means that all your power tubes need to be replaced at the same time. This isn’t so bad but you want your power tubes to be new to match the hours they are meant to last.

Preamp tube

If the sound is dropping-out on only one channel, it will be one of these tubes. Noise can come from reverb tube too, then that needs to be changed

Rectifier tube

If you like having the old school rectifier tubes, these also can be replaced one at a time.

Main power fuse gets blown

If there’s a bad fuse or rectifier tube that’s blown, you’ll need to change both of them.

Main fuse keeps blowing

If your main fuse continues to blow then there’s a serious internal problem. This is the only time you need to take it to the repair shop.

Are there other reasons volume loss is happening?

One last thing I need to mention is something called Buzzing-out’. This is for amps that have a built-in FX loop.

You can have volume loss from this feature too. Just clean the FX send’ jack with a contact cleaner.

Attach a short jumper cable into the FX send jack and the other end goes into the FX return’ jack. This should cancel out the volume loss problem after that. And even with your control knobs can have grit or dirt built-up on them too.

You’ll need to use a switch cleaner lubricant. This helps clean off the contacts under the knobs to remove that heavy build-up. If you’ve had volume level problems before, this is another hidden gem that most repair centers don’t tell you about. A can of this stuff will cost 8 bucks.

Dirty Tube sockets need to be cleaned too. Any time you change a vacuum tube, you need to clean those little prongs so you have really good contact. It there’s any kind of dust or dirt on a new tube, it will affect how well they have a contact inside your amp. It wouldn’t hurt to remove all your tubes and spray the inside connections also. Give this stuff at least 15 minutes to dry off before using your amp. After that, your amp should work better than ever.

All vacuum tubes have a life to them. They won’t last forever but I’ve put together the average lifespan they tend to last. If you decide to invest in your equipment, look to buy in bulk.

The below option from Amazon is a pretty good deal.

Buy them in bulk to save money and keep a brand name the same. And only use tubes that are top-shelf for quality. Here’s what you can expect for how long they last.

The lifespan of the power tube

RL84: 500 hours

6L6, 6V6, 5881WXT or EL34: 1000 hours

The lifespan of preamp tubes: 1000-5000 hours

The lifespan of Rectifier tubes: 100-200 hours for new Mullard tubes (older Mullards lasted up to 80,000 hours)

My final thoughts

Why does my tube amp lose volume? If there’s going to be a problem with your amp that has volume dropping, it can always be fixed with these tips. Just be sure that you’re smart about unplugging the amp before you do any tube replacement.

Nobody ever got famous for being fried by a live amp. I’ve been shocked before and it feels like being sucker-punched with a 2×4! You don’t want to make that mistake, so always double-check your plug. Just to let others know you’re doing repairs, wrap a bright yellow electrical tape on the end of the plug. Save that electricity for the next gig instead.

Rob Wreglesworth

Rob has come to terms with the fact he will probably never be a famous rock star....but that hasn't stopped him from writing and recording music in his home studio. Rob has over 15 years experience of recording music at home.

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