how to know when and which tubes are bad?

[tempest1226]

hey everyone. Im convinced that i need a retube after posting my situation of my sound change here on the forum but now ask the question. How do i know which tube(s) are bad in which spots. Is there a tester that you can buy and do yourself or do you absolutly have to take it somewhere. I just cant imagine that you would have to change all the preamp tubes, rectifier tubes, and power tubes if its just a couple preamp tubes. or is the newbie wrong. haha. let me know and thanksss

 

[Rayder]

even though one of your tubes are faulty/broken, it is best to replace all of them, so that the tubes are matched (preamp or poweramp)

 

[tommyhawk13]

Is there a pretty blue color inside the tubes?

 

[tempest1226]

no i dont see any blue in the power/recto tubes. BUt i also wanted to ask, how do i get to the preamp tubes to see them because there is these metal casings around them. Any details would be awesome thanx. -ron

 

[ylo]

You can often tell whether a preamp tube is going bad just by gently tapping on it (with the amp on) and listening for funky noises coming out of the speakers. Power tubes are not so easily diagnosed by tapping. In my experience they just begin to sound a bit dull and dead after a few hundred hours, so I replace them.

 

[Russ]

Your preamp tubes should outlast your power tubes by at least couple a couple changes depending upon the tubes and how hard you push it. Some NOS tubes will never need changing for the life of your amp in some positions. Usually your amp will start changing the way it sounds when you need to address your tubes. Noisy tubes will need to be changed. Microphonic tubes will need to be changed unless you like the howl. A dead preamp tube may keep your amp from even running depending upon its position in the amp. Power tubes will start to do weird things like cut in and out or be just low overall. Sometimes they can fail while your are playing. This is bad. Normally you get a warning from a fuse that it is time to get your amp checked because something is wrong. Most of the time you can replace your power tubes and you are fine. Sometimes you can even reseat your old power tubes and check your cabling to remedy the blown fuse.

If a power tube fails or needs replacement replace at least the pair with a matched pair. If your amp has more than a pair then try to replace them all with a matched quad or sextet. If a preamp tube fails it is up to you to decide how many you want to replace. More often than not your amps stages that create your gain get the worst beating. V1 most often gets killed. This is also the most important tube in your amp because it sets the primary tone. Sometimes you can get away with moving your preamp tubes around playing musical sockets until you figure out your best sounding reconfiguration. This is a great temporary fix for a noisy or microphonic tube. Obviously the best fix is to just replace it. If you like the sound you were getting prior to you tube troubles replace your tubes with the same stuff. If you weren't happy, then you have a great opportunity to explore other tube flavors.

 

[Russ]

even though one of your tubes are faulty/broken, it is best to replace all of them, so that the tubes are matched (preamp or poweramp)

Preamp tube matching isn't necessary with Mesa. You don't even need a matched phase inverter. In fact, some here even find a mix of tubes from different manufacturers to be very nice.

 

[Russ]

no i dont see any blue in the power/recto tubes. BUt i also wanted to ask, how do i get to the preamp tubes to see them because there is these metal casings around them. Any details would be awesome thanx. -ron

To access your preamp tubes you need to remove the metal shields if they are covered. You just push the shield down slightly and turn it counter clockwise a little. It will pop up a little bit after you clear the lock. Then lift the shield off. Your tube will then be exposed.

You might have to remove your power tubes to actually get your hands in there. Be careful to note which power tube went where because you don't want to mix them up.

A final word of caution. Tubes get hot. Hot tubes can burn your skin. Let them cool down before handling.