Tube Troubles

[Discoqueen]

Hey y’all

The amp in question is an Orange th30. I was playing earlier with my drummer and my amp sounded absolutely awful. I read up and it seems that perhaps a preamp tube is the culprit. I read that you have to replace 12ax7s in matching pears, so does that mean I should replace all the 12ax7s?

I think 1, 2 and 3 are the ones I need to swap out, can I just change one or do I need to change a few?

The sound was lacking low-end, it sounded uncharacteristiclly honky and weak. Does that sound like a preamp tube issue?

Ah yes, a weird thing about this amp that I probably should have put my thought into, when you turn it off it makes slight clicking sounds. Not through the speaker, just from the amp itself. Obviously it’s one of the tubes because... I think I’ve heard fluorescent bulbs make that kind of hollow clicking sound. This would probably also indicate that my issue is tubes?

Thanks

 

[DudeManBrother]

You can replace preamp tubes individually as needed. When the amp is cooled off: make sure each tube is fully seated in their tube sockets. Then you can power it on. You should notice a subtle orange glow in each tube. If they’re all glowing, then you can tap each tube with a chopstick or pencil. A microphonic tube will really ring out and feedback.

Power amp tubes, EL84’s in your case, should be swapped in matched pairs. The glass ticking is normal with tubes as they cool off. They should have a nice orange glow with a subtle bluish color. If you see bright red running up the center, or feel excessive heat, then it could be failing tubes or something in the amp causing the tubes to fail.

Power tubes typically need replacing far more often than preamp tubes; but tolerances suck now adays so there are no guarantees as to longevity.

 

[gnoll]

All preamp tubes aren't actually supposed to glow though, right?

 

[DudeManBrother]

All preamp tubes aren't actually supposed to glow though, right?

They all have filaments so they will all glow, but not necessarily very bright.

 

[Discoqueen]

You can replace preamp tubes individually as needed. When the amp is cooled off: make sure each tube is fully seated in their tube sockets. Then you can power it on. You should notice a subtle orange glow in each tube. If they’re all glowing, then you can tap each tube with a chopstick or pencil. A microphonic tube will really ring out and feedback.

Power amp tubes, EL84’s in your case, should be swapped in matched pairs. The glass ticking is normal with tubes as they cool off. They should have a nice orange glow with a subtle bluish color. If you see bright red running up the center, or feel excessive heat, then it could be failing tubes or something in the amp causing the tubes to fail.

Power tubes typically need replacing far more often than preamp tubes; but tolerances suck now adays so there are no guarantees as to longevity.

Ah, thank you! Can I tap the power tubes as well to see if they are bunk?

 

[mnemonic]

It could be either power tubes or preamp tubes, both can potentially cause loss of bass, bad tone, volume drop, etc. Power tubes seem to fail more often than preamp tubes though.

It could also be something else, even as simple as a dirty jack or busted cable.

Tapping tubes is more about finding ones that are microphonic. They’re all microphonic to an extent, but if you tap it and sounds like a ringing bell, it’s probably too microphonic.

If you have a known good 12ax7, you can swap it into the various slots, one by one, to see if one preamp tube is the problem.

Since the th30 has a low power option that disables two tubes, does this bad tone continue when you switch to low power? If so, try swapping the tube pairs around (swap tubes 6 and 8 with tubes 7 and 9).

If that fixes the problem, you’ll know it’s a power tube.


A visual inspection to check for red plating, arcing in the tube, etc is also a good idea. If there’s lightning in the tube, it’s a bad tube.

The circled tube below is redplating:



This is either a problem with the tube, or a problem with the amp (usually a fried resistor or something). You can check by swapping that tube around with another.

If the redplating follows the tube, it’s a bad tube. If it stays with the socket, it’s a problem with the amp and you should take it to the tech to have it diagnosed.

 

[777timesgod]

The pre-amps glow, close the lights in your room and turn the amp on to see them.
It is normal to hear a tube sound when the amp is turned off. The change of temperature is the cause of this as they cool down, it is a glass container after all. You definitely need a tube change if the sound has taken a dive, if the change does not fix the problem a technician will be needed but I doubt you will reach that point, as what you mention is the general tube wear symptoms.
Some people change all their tubes to keep all sides of their amp sounding fresh and balanced but you do not necessarily need to do so. It is a good idea to change the pair though, they work together and if one is unreliable it will drain the other quicker. Keep in mind that the more you drive the amp's volume the faster you will see degrading in sound over time. Lastly do not forget to select the same pre-amp type 12AX7 and not T7 or U7, you may switch brands though if you want something different. Let us know if this solves the problem and turn off the amp for the change process, some do it with it in standby mode but it is safer to do so without a current going though.

 

[KailM]

Since your amp has an effects loop, plug your guitar directly into the "return" jack and turn it on. If your power tubes/power section is still good, you should hear a loud and clear clean tone, though your amp settings will not be able to affect it. If it sounds loud, and clear, the power tubes are most likely fine, and your issue may be with a preamp tube.

Usually, preamp tubes don't all fail at the same time. So you can buy one new tube and cycle it through all the positions to find the culprit.

Is the tone bad on all channels? If so, it's more likely to be a power tube issue. One of the trademarks of power tubes going bad is that your low-end goes away and the distorted tone becomes very brittle and harsh. You may also find that you can't get the volume as high as it was before on the same settings. However, with an intact preamp section, you should still hear plenty of gain.

When a preamp tube goes bad, either one or both of your channels stops working, or your gain is drastically reduced.

 

[efiltsohg]

A visual inspection to check for red plating

red plating is a tube that is overloaded & going to fail, not one that already has

I doubt it's a power tube issue because that usually gives you no sound and/or blows a fuse

 

[Discoqueen]

Thank you all for the very valuable insights! I will be be working on the amp for a little while tonight with the info y’all gave me, and I have a 12ax7 on the way. I will update when I go through a few of the suggested actions. Thanks again

 

[Discoqueen]

I replaced one of the gain channel 12ax7’s (number two on the picture on the OP) and that seems to have cleared things up. Sounds much better! Thanks for the help!