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HELP!!! Mesa 5:50

Messages
136
I bought a Mesa 5:50 about 2 weeks ago, it's worked perfectly until now, i just plugged it in, let it warm up, and turned it on and it make a really bad crackling/hiss/hum sound. What is going on and what do i need to do??? Any help is greatly appreciated.
 

Stu Blue

Member
Messages
3,167
Tim The honest answer is you phone round and find your nearest amp tech and get him to fix it.
 
Messages
136
yup, FYI, i went to the mesa website and they said to pull one preamp tube at a time and and if that was the problem. I done that and it's not...
 

Audioholic

Member
Messages
2,573
You have to replace the pulled tube, rather then just taking one out. Do you have any extra tubes laying around? make sure they are all sitting in properly, sometimes they can come slightly out of socket.
 

torquil

Member
Messages
1,636
I second the suggestion about taking it to an amp tech.

If you are not afraid of blowing more tubes you could simply try to put a new set of power tubes in. You probably need som spare ones anyway.

There are a few things you could do to troubleshoot yourself. Since you have an FX loop, you can send the preamp signal to another amp to see if it is OK. Or you can use just the power amp section by sending something into "FX return". This could help you locate the error. To be sure that the FX loop is enganged in both cases, it is wise to insert plugs in both "send" and "return" jacks when doing this, even though you are only using one of them at a time.

Another thing is to try the amp in class A mode. If it doesn't get better, try to exchange the two power tubes (just change places), and then try class A mode again. If it only works in one of the configurations, then one of the power tubes are broken. In class A it only really uses one of the power tubes, but I don't remember which one.

But don't blame me if your amp is damaged by any of these actions.... Tube defects can lead to damage in several other components.

I'll mention that Mesa Boogie says that one should not run the amp with only one power tube, in class A mode. Of course not in full power mode either...

Also, I think Mesa Boogie includes a section on tube debugging in each manual, so you could look for that. It contains some useful info.
 

torquil

Member
Messages
1,636
One more thing. If you find that the amp works in class A with only one of the two possible configurations of the power tubes, I would still not use the amp like that for more than just a short while (to hear that it works). I think the amp needs both tubes installed, even if it only uses one tube to amplify the signal in class A mode. I was just reading up a bit about these things.

An amp tech is probably the best option, especially if it doesn't work with new tubes.

Hope it is up and running again quickly. Mine is a 5:25. A fine amp!
 

furry

Senior Member
Messages
1,399
crackling/hiss is probably just a bad preamp tube. buy yourself a $10 12ax7 and sub out the preamp tubes till you find the bad one.
 

Waxhead

Member
Messages
6,244
Sounds like just a preamp tube to me Tim.
You can do it yourself or take it to an amp if you're unsure.
Read your manual. Mesa amps do not need rebiasing when you change tubes. If you do change tubes I recommend you spend $100 and do the full set with these tubes recommended by Doug of www.dougstubes.com

Preamp
V1 - Tung-Sol reissue 12AX7
V2 - High gain JJ ECC83S
V3 - Penta Labs 12AX7C
V4 - Shuguang 12AX7C9
V5 - Sovtek 12AX7LPS

Poweramp - two SED 6L6's

these tubes will improve the tone, make it smoother, give you more gain and reduce amp hum by over 50%. You need a spare set of tubes on standby anyways. I keep the old Chinese Mesa tubes in a box :D
 

torquil

Member
Messages
1,636
If you are going to swap between preamp tubes, you can ignore V5, which is the reverb tube. So if you have one bad preamp tube, you still have four good ones for use in positions V1-V4, making both channels work. I think it only means the the reverb will be missing. See the manual for tube names/positions, on page 24.
 




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