how to find a bad tube?

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tom18222

yes
ok, so heres the thing. i made a topic last week about me mesa dual recto roadster with a blown tube.


i bought the amp online, so i cant return it, id have to spend 200 for shipping both ways. the tubes are under warranty for 5 years, so if i can find out which one went, hopefully i can get a new pair sent.


so, basically, how can i troubleshoot to find out which tube is bad.
 
How do you know the tube is blown? The symptom will tell you if it is a preamp tube or a power tube.

If it only happens on one channel, it's a preamp tube. If it always happens, it's a power tube.

You have 6 power tubes that you can use in varying combinations. Try the combinations to determine which one isn't working.

You can also look at the tubes. If one is glowing differently than the others, that is probably the one.
 
You could try to narrow down whether it's a bad preamp or power tube. Plug your guitar and a pedal into the FX return jack and see if you get a signal through the power section.
 
thats what i did, i get a signal from the fx return, so it has to be a preamp tube.

i just dont know which one:(
 
Do any of the channels work? Some of the preamp tubes only work on certain channels.
 
You could always just go out and buy a 12ax7 and swap it with each tube until the amp works. They are only about $12/each.
 
Farview said:
You could always just go out and buy a 12ax7 and swap it with each tube until the amp works. They are only about $12/each.
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+1 Yep that's the best way to do it. I'd get at least 3 new 12AX7 tubes because you should always have spares handy.
 
the amp has 6l6s, they are compatible right? should i get a matched pair or one?

does guitar center sell them?
 
tom18222 said:
the amp has 6l6s, they are compatible right? should i get a matched pair or one?

does guitar center sell them?
Click to expand...
You have three different types of tubes in that amp.

The 6L6's are the big power tubes, you have 4 of those.

The 12ax7's are the small skinny tubes inside a shiny silver tube/cover. That cover comes off with a 1/4 twist counter-clockwise. They are the preamp tubes, you have 6 of those.

The 5U4's are the rectifier tubes, you have two of those.

If you go out and get a couple 12ax7's, you will be able to look at them and see which tubes are which inside the amp
 
another thing to be aware of is do any of the tubes look kinda cloudy??? that means that air is getting into the tube and that wold be the bad one... try simply jiggling the tues to make sure they are well seated also... either of these can be aproblem with an amp that just went through shipping... also with this beinbg a new amp check your yellow pages for an independent repair shop(not store affiliated) and have them do it if they are boogie certified...
 
I just bring the amp to my fav. shop and use his tube tester. It's free, so I do it all the tubes when I buy a new (to me) amp, just to be sure.
 
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