developed noise in Mark V at startup

[BluzCruz]

When I first power on my Mark V, I get some crackling and whooshing. It's still there with input cable removed, so not external source. It's present on all channels, more noticiable as power settings go up from 10->45->90W. Seems to be on all modes, at least in channel 1 - didn't try them all on channel 2 and 3. I usually ignore it and start playing and within a few minutes it's gone and stays gone....maybe 5 min at most. Maybe I just need to warm up powered on in standby longer?

Or should I suspect pre-amp tube failing, and more specifically V1?

Anyone have experience with a similar problem?

I noticed those preamp tubes are a pain to get to without pulling the amp out of the cab...guess I have to move it to a workbench or table where I can get at it a little better I haven't had the amp that long and it's only a couple years old, so this is the first time actually really thinking about changing tubes in it...first time I pulled the cage off.

 

[jaslan]

This could be a sign of power tubes starting to show signs of wear. How old are they?

 

[fr0sty]

I always gotten a little buzz noise through the speaker when powering on (in standby). I can recreate the noise when switching power modes on the amp (still on standby).

 

[doublescale1]

This may be too simplistic but but I'll throw it out there: are you taking the amp off standby at the same time as you you flip the power switch on? If so, you may just be hearing the capacitors "spooling up" with power. Leaving the standby switch engaged while powering up will keep that noise from coming through to the speakers. That was something I was doing with a Carr Rambler I have, heard a kind of white noise swell, up and down then it would be gone - I was just getting lazy and throwing both power and standby switches at the same time. Once I did power, wait 20 sec. then standby off, everything stayed quiet.

 

[BluzCruz]

Thanks for the replies.

The power tubes are 2 years old or less. The head is a 2016, not sure what month. And they have not seen very much use. It was shipped across country once, and it has been moved around a few times. So possible a tube got jarred and damaged.

I don't have any noise in standby mode. Just when I turn the amp fully on.

I normally wait about 30 seconds after powering on before coming out of standby.

 

[jaslan]

I play 5 to 10 hrs a week and start getting crackles after about a year. Put in a new set and see if it helps. Even if it doesn’t, you will have a spare set ready to go.

 

[BluzCruz]

I don't do wholesale tube replacements trying to fix problems without diagnosing the problem. It's usually not the tubes, and when it is a tube, it's usually only 1.

I tested all the pre amp and power amp tubes on an Orange VT1000 tester, they all passed just fine. I realize that does not rule out microphonic or otherwise noisy tubes. I will do tapping testing in the amp, as well as visual inspection of the tubes in the amp with the covers off...but haven't yet.

I can't test the rectifier tube, but a visual inspection shows some discoloration on the glass near the top plate, and the top plate looks slightly darker than the bottom plate. I don't know if that is a failure indicator or just normal on the 5U4GB.

Anybody have comments on what happens as the rectifier tube gets weak or approaches failure? Don't know that there is an issue but the discoloration is suspect to me.

 

[mace]

I’ve had several rectifier tubes go out on the Mark V in only 6 years. Not sure why. Anyway, one indicator is when there is a blue flash from the rectifier tube when you power on the amp.

 

[jaslan]

I don't do wholesale tube replacements trying to fix problems without diagnosing the problem. It's usually not the tubes, and when it is a tube, it's usually only 1.

Just to clarify, I didn’t mean swapping all the tubes, just the power tubes or even just one pair of power tubes, which could help identify the problem. For what it’s worth, a Mesa tech told me power tubes should be replaced in matched pairs and that an old “yellow” tube may not necessarily match a new “yellow” tube. Thus, replacing just one power tube was not recommended unless the remaining matching tube is relatively new. Of course, it doesn’t apply to pre-amp tubes.

 

[bandit2013]

I had considered getting an Orange VT1000 tube tester. That may check for obvious issues with preamp and power tubes at specific plate voltages or what ever else is done to test the tube. However, a tube may pass with flying colors on a tester but not turn out to be ideal in the amp. As for preamps, each triode may be operating at a different plate voltage depending on its location. Each voice on all three channels will remap some of the circuits such that the gain setting may be too much for a weak tube resulting in noise or popcorn effects. Testers are great but may not reveal the issue when used in the amp. However I would rather fail or short out a tube in a tester than the amp. Pops and crackles or noisy sounds at turn on time when switching that standby switch may have some noise effects especially with the channel master volume controls or the global master volume control. This may last for a brief second or two as some preamp tubes may not be up to full temperature on the heater, circuits may not be properly loaded, and some circuits may not have proper charge on some capacitors. One reason for some pops when switching channels after startup since the strobe mute will not swamp that effect out. This issue is more prone with a Roadster than the Mark V but does not mean it is immune. I normally find the volume controls to sound scratchy after startup but that goes away within a second or two. If things are taking longer to warm up, that is a good sign to change tubes. A cathode can only emit so many electrons before it is done and has an operating life depending on how it is used. All parts of preamp and power tubes change over time. When they start to degrade in performance, it may effect others that are ok or in need of replacement. If you have a head, yeah the preamp tubes can be a pain to get at. You can always place the head in a different position to get better access to them. Remember the orientation of the preamp tubes when you pull them out. The position of the missing pin on the 9 pin preamp tube would be facing the front of the amp (V1, V2, V4, V5, V6 and V7), note that V3 has the open space pointing to the rear of the amp. Generally speaker, may be in need of tube replacement. If and when you do decide to replace any of the power tubes, always good rule of thumb to replace the Rectifier tube too.

 

[Sicman71]

Did you ever figure out what the problem was? I have the same issue.

 

[MarkV User]

For what it's worth I had issues like the on described that I fixed by replacing the low voltage diodes. I don't know what the mysterious crackling sounds were for me, but probably a relay was toggling between open and closed due to insufficient voltage from the low voltage supply. I didn't figure it out until later when the low voltage supply completely failed with two bad 1N4007 diodes. Replacing the diodes fixed several annoyance issues: foot switch and channel switching not working consistently, crackling as you observed, and eventually no power light or sound out of the amp.

This might not be the most likely cause of your problem, but may be worth considering. And by the way, I replaced the power tubes when I changed the diodes, so it is possible that a bad tube was the cause of my crackling. If I remember correctly, moving power tubes around and tearing with just two tubes didn't affect the crackling problem though.