Mesa Triple Crown TC-50 2nd & 3rd channels noisy

[maxem]

Had posted this on another page that had a discussion about this issue and thought I’ll check the Mesa forums while I wait for Mesa support to get back to me.

Channel's 2 & 3 on my TC50 are noisy (crackle & hiss)...channel 2 isn't too bad but there's a lot of crackle & hiss on channel 3.

I tried swapping out the V3 & V4 tubes that correspond to channels 2 & 3 as per the manual, with new tubes and it did not solve the problem. I also tried swapping the power tubes with new ones and that didn't help either. Also tried replacing the other 12AX7 tubes and the 12AT7 but had no luck.

The noise is there even though no guitar/cable is connected to the input!!

Is there something else I could try and/or am I missing something?

 

[jnoel64]

Did you try swapping out V1? That's the main input stage for all three channels, isn't it? I use the SPAX7 in V1 in my TC50. Mine is a very quiet amp, regardless of gain level or channel. Yours does not sound like a "normal" situation to me.
I've posted this before, but my 12AT7 had bent pins from the factory. Never noticed until I pulled it. I replaced it with a JAN-Phillips 12AT7 just to be safe. But that's just for the loop, isn't it?

 

[maxem]

Did you try swapping out V1? That's the main input stage for all three channels, isn't it? I use the SPAX7 in V1 in my TC50. Mine is a very quiet amp, regardless of gain level or channel. Yours does not sound like a "normal" situation to me.
I've posted this before, but my 12AT7 had bent pins from the factory. Never noticed until I pulled it. I replaced it with a JAN-Phillips 12AT7 just to be safe. But that's just for the loop, isn't it?

Believe V1 corresponds to channel 1 as per the manual. I did try swapping that and the other 12AX7's and 12AT7 but had no luck. No damage to pins or sockets from what i can see.

Temp fix i have is a noise gate in the effects loop but need to get this fixed. Have to send it in to get it looked at/serviced

 

[JPBoogie]

Hello Maxem, this will sound silly... just doing some elimination process here. Since you have tried with the tubes and nothing worked... Have you changed where you plug your amp recently? Have you changed anything in your house (i.e. modems, routers, lighting, etc)? I ask because I got an awful crackling noise once because my router was on the same circuit braker than my Boogie. Almost sounded like someone was making popcorn LOL. Anyway, hope this helps.
Oh, have you tried replacing your power tubes? Those channels are high gain so would amplify any noise on the line... would you get the same noises if you put a boost in front of Channel 1? Let us know what you found please and good luck fixing it, hopefully not an expensive solution.

 

[Eevil]

Had posted this on another page that had a discussion about this issue and thought I’ll check the Mesa forums while I wait for Mesa support to get back to me.

Channel's 2 & 3 on my TC50 are noisy (crackle & hiss)...channel 2 isn't too bad but there's a lot of crackle & hiss on channel 3.

I tried swapping out the V3 & V4 tubes that correspond to channels 2 & 3 as per the manual, with new tubes and it did not solve the problem. I also tried swapping the power tubes with new ones and that didn't help either. Also tried replacing the other 12AX7 tubes and the 12AT7 but had no luck.

The noise is there even though no guitar/cable is connected to the input!!

Is there something else I could try and/or am I missing something?

Have you tested plugging guitar straight to fx return? Does it crackle then? Just to check if the noise is coming from preamp or power amp..

 

[bandit2013]

Hello Maxem, this will sound silly... just doing some elimination process here. Since you have tried with the tubes and nothing worked... Have you changed where you plug your amp recently? Have you changed anything in your house (i.e. modems, routers, lighting, etc)? I ask because I got an awful crackling noise once because my router was on the same circuit braker than my Boogie. Almost sounded like someone was making popcorn LOL. Anyway, hope this helps.
Oh, have you tried replacing your power tubes? Those channels are high gain so would amplify any noise on the line... would you get the same noises if you put a boost in front of Channel 1? Let us know what you found please and good luck fixing it, hopefully not an expensive solution.

Yeah, this is good advice.

I have a BAD100W that gets a lot of use. I never hear any noises such as a bad preamp tube (typical popcorn noises) except when the guitarist comes over to jam, the amp sounds like it has bad preamp tubes and is going to die any time during our practice session.

Turns out he forgets to take out his cell phone out of his front pocket. He also tried placing it on top of the amp, that made the noise in the amp far worse. Cell phones will also make odd noises occur in the amp and when they are not present all is good. Effects that have batteries can do this too if the battery is low. Same with active pickups in a guitar if the battery is on the weak side.

 

[JPBoogie]

Hello everyone!
Well it looks like it's my turn to have this issue now... @maxem what was your fix?
Channel 1 is dead quiet. CH2 is kind of noisy and CH3 is noisy. For both CH2 and CH3, the more I crank the gain, the more white noise I get.
I have tried to swap each preamp tubes one by one with a new tube and nothing. I have then tried the power tubes swap for new ones, nada.
I tried different cabs with either 8 or 4ohms, nothing. I also swapped both V3 and V4 with new tubes... nothing. This white noise was definitely not there before and I am utterly annoyed. I turned the lights off, moved the head to different areas, nothing. This noise is there with or without the instrument plugged in. I also took the send/return cables on/off, footswitch plugged/unplugged... zero change: HELP!

 

[JPBoogie]

Hello everyone!
Well it looks like it's my turn to have this issue now... @maxem what was your fix?
Channel 1 is dead quiet. CH2 is kind of noisy and CH3 is noisy. For both CH2 and CH3, the more I crank the gain, the more white noise I get.
I have tried to swap each preamp tubes one by one with a new tube and nothing. I have then tried the power tubes swap for new ones, nada.
I tried different cabs with either 8 or 4ohms, nothing. I also swapped both V3 and V4 with new tubes... nothing. This white noise was definitely not there before and I am utterly annoyed. I turned the lights off, moved the head to different areas, nothing. This noise is there with or without the instrument plugged in. I also took the send/return cables on/off, footswitch plugged/unplugged... zero change: HELP!

Bump

 

[sPernils]

A long shot, but V1 are involved even in ch 2 and 3. It’s the front end tube. Try to replace it with a good 7025 tube or the new Mesa SPX variant of the 12AX7.

 

[JPBoogie]

A long shot, but V1 are involved even in ch 2 and 3. It’s the front end tube. Try to replace it with a good 7025 tube or the new Mesa SPX variant of the 12AX7.

Hello and thanks for reply; I tried that yeah... and no luck. I even got to the point of replacing all 7 preamp tubes and power tubes. Nada!

Cheers,

 

[rarebitusa]

You've swapped tubes but maybe try to isolate the issue? Like @Eevil mentioned earlier. Just run the fx send to something to monitor and maybe see if it is just in the preamp section? Alternatively you run a signal into the fx return and see if it is power section related. But with it being most noticeable on Ch 3 it's a longshot.

Does any of the CH3 voicing selections make any difference?

 

[JPBoogie]

Hello and thanks for the reply.
I will try the Fx ideas and see... if the head comes back from the tech without being fixed. The voicing on any channel had no impact on the white noise; just gain and the tight toggle.
I will report back here with what the tech found.

Cheers,

 

[bandit2013]

I can tell those that are not familiar with the Triple Crown, same comments for the RA100 but that amp has the role reversed with the tubes.
There are a few Mesa amps that make use to two separate preamp sections that do not interact with other stages. Meaning that with the TC, V1 is only used on the clean channel and not associated with the Hi/Lo gain circuit at all. Same for V2. you can literally remove V1 and V2 and still use the hi/lo gain channels. The RA100 is different that the hi/lo gain circuit is V1 and V2 and the clean is V4 and V5. The FX circuit would be V3. No big deal. Most will think that V1 is common as the first gain stage in any given amp. I did make some graphical signal path diagrams for aid to amp in some diagnostic help. Here is the TC series. All channels included. The preamp does not make use of all tubes in a cascaded format like you would find in a Mark or Rectifier design. The first gain stage for Hi and Lo channels 2 and 3 will be V3A. V1 and V2 are not used except for the clean channel.

I can make the assumption that the 4 triode cascade of the TC is similar to the RA, the triodes will all have a 100k plate resistor. The first three gain stages will also have a 10uF bypass cathode cap. That will ramp up the gain factor. I could describe each gain stage if needed but I am working from the RA100 schematic and not one of the TC which I do not have. V5 can be a contributor to some noise as the send circuit is a cathode follower. The noise is more or less from V3 or V4 or both. Also, there are a few op-amps that follow the triode gain stages. The clean only has the TL072 which is a FET type of op-amp. The hi/lo channels also make us of this circuit but also have a different chaser op-amp 4558D which is a high gain type with NPN transistors. Op-amps will create noise as they will have a much higher gain factor than a triode gain stage. I simplified the diagram above with a single op-amp buffer, it is far more complex than that. Preamp tubes do age just like any other tube. They may become noisy, change or shift in tone. etc. The solid-state buffer circuits will not age like a vacuum tube. Reducing the noise floor with better preamp tubes may help the issue. the Mesa branded JJ ECC83s tubes are not perfect or quiet by any means. Some of that could be related to the wires inside the cavity and how they are resting in place. Just moving a wire or bending it towards the PCB may result in noise issues. The noise floor will be there but should not be most of what you hear. I get that noise with the amp without anything plugged in except the speaker and power cable. Badlander, Roadster, MWDR, Mark VII, Mark V90, JP2C, TC100, TC50. Even the Mesa TT800 which does have three preamp tubes but is mostly solid-state Class D power. It is all about acceptable signal to noise ratio. Some tubes can be noisy or get worse over time. Also have to consider that some of the components in the amp will also change over time due to thermal drift or thermal cycles from operating the amp and turning it off and the parts cool down. Carbon comp resistors can form small cracks, capacitors drift in value, etc. The Guitar amp is not perfect but that is what makes it sound good. Sure, noise floor issues can be an issue. Just play through an EVH 5150 Stealth III EL34 100W amp and you will know what I mean, that amp is all noise floor. Still, there may be some resolve in selecting some tubes with a slight gain difference. No point in going full tilt with high gain tubes as the op-amp circuits will compensate. There is some merit to the 7025 tubes, even some with the MG designation for medium gain. Not sure if a 5751 tube would be appropriate as it will have a 30% reduction in gain factor.

 

[bandit2013]

Hmm, one question comes to mind. Are you using the tight switch? I found that adds a considerable amount of noise to the amp. The drive switch on the clean is desired, I do no care much for the tight switch on Hi/Lo as I feel it is as useless as the shred mode on the JP2C. I did not feel it was necessary to use it even with the 7-string baritone axe I use. Just a thought and observation.

 

[bandit2013]

I got out the TC50 this morning and pulled out the chassis. First power up in some time. Odd that the amp was fading in and out. I knew exactly what that was, V5. I had an old JAN/Phillips 12AT7 I had used in the Mark V90 for the saturation mod trick. It tested ok but one of the triodes was on the weak side. I replaced it with a balanced RFT ECC81 (12AT7) as it has a darker tone to it. Well dang did that not wake up the cows in the next county. Forgot how loud this TC50 is. Since I disconnected the reverb, I added a digital reverb in the FX loop.

I did test the V3, V4 and V7 tubes to verify they were still good. They tested fine. Testing, well if you count the Orange Valve tester a form of testing, then fine. At least I get some representation where each triode resides with a number and if it is worn or good. I also ran tests on the NOS tube I had on hand in the 12AT7 category, one was bad. It is possible it came that way or it could have been the one I abused in the RA100.

Well, something rather interesting developed. I may have swapped some of the Mesa branded 12AX7 tubes after getting the amp but these have been in there since I got it in 2017. Power tubes on the other hand, I still have the originals but what is in the amp may not be them. I have cycled many power tubes to see how different a 6CA7, EL34B, and so on. It was the STR450 that killed the amp and it required servicing but it was not power tube related according to Mesa. It was just coincidental when the STR450 blew the fuse, and the amp did not work after replacing the tubes and fuse.

Anyhow. I could not get the noise floor on CH2 or CH3 to the point of annoyance. Sure CH3 did have a slight hiss to it when you cranked up the gain. Did not seem to influence the overall sound or make it fizzy. Even tight mode did not seem to be an issue. Normally all it would do is cause the amp to feedback. Not this time around. Go figure. Not sure if having the reverb circuit disconnected has anything to do with that since you will get feedback if you have two cables plugged into the FX loop but not connected to anything, that is from the reverb circuit.

Took the image after I replaced V5 with an RFT ECC81 tube.

Here is a closer look. Hard to tell. Rest assured it is an RFT 12AT7. This amp is quiet on all channels. The only thing I changed was V5 and have the reverb disconnected. I am using the FX loop with a Strymon Bigsky MX pedal. I am surprised that the tight modes did not do much in terms of noise. I do plan on trying out some JAN/GE 12AX7WA in V3 and V4, also the JJ E83CC frame grid tubes. Other tubes I have tried did not make any difference. Will also have to give a try of a Mullard Long plate 12AX7 (reissue) in V7 but for now, the stock tube will suffice.

At least I had an opportunity to dust off the chassis with a dry paint brush. This amp was dusty and needed a bit of cleaning. I should clean up the dust on the front panel too.