Mesa Mark V problem (popping/scratching sound)

[lj678]

First of all, my apologies if i'm posting this in the wrong place.

I've made an account here specifically for advice on my Mark V which has recently began producing a popping/scratching sound on all three channels once I come out of standby.

I've never had any issues with it in the 5 years that I've owned it (never had it serviced either :shock: ). I don't ever plan on selling it however it's not had much use recently due to moving house, however I noticed that one of the Mesa 6L6 power tubes wasn't glowing (although I didn't notice a difference in tone) so I went online and ordered a quad matched set of Electro Harmonix EL34s(I always wanted an excuse to throw EL34s in this beast). Now the EL34s I bought aren't Mesa branded so I liaised with the tech who sold me them who informed me he had lots of experience with Mesa amps and the plate current on this set would be perfect for the Mark V (AFAIK they all have a plate current of 43mA).

Anyway fast forward another week i've installed the tubes (yes the bias switch it now on EL34 mode) and I'm getting a lot of popping/scratching sounds from the amp when it's idle and is still present when nothing is connected to the front of the amp (i'll attach a YouTube link of a quick video I shot on my phone displaying it). However aside from the popping it is producing a great tone. I've tried various ways of trouble shooting with using the hard bypass switch, rolling the reverb off, tried every power setting on each channel and even using a different speaker cabinet. I've tapped on each of the EL34 power tubes and it isn't making any noise, which is leading me to believe it could be a preamp tube issue (maybe even the rectifier tube)? The preamp tubes and rectifier tube are as old as the amp which was made in April 2010.
I'm thinking of buying a custom set of preamp tubes to tweak the tone further but I just want to know in advance if this will most likely solve the issue.

https://www.youtube.com/watch?v=1-N1Cj_Xors&feature=youtu.be

 

[jb's 52]

Sounds like a pre-amp tube.
In general, I think scratchy and poppy = pre-amp, whereas volume fluctuations = power tubes.

 

[Bankim]

Nice Try on Mirroring the static noises.. LOL.. Nice playing too..

If the noise/pops are on all channels, change V1 preamp tube first. Many people prefer the Mesa SPAX7 in the V1 position on the Mark V. I use the plain old Mesa 12AX7 tube.

And welcome to the forums !!

 

[bandit2013]

Most likely preamp tube. But it can also be the Rectifier tube (usually not the case).

Tubes that affect all channels (reverb off, FX loop in bypass) V1, V3, and V7, with the reverb on, that would include V4 and V5, with FX loop enabled that will bring in V6. V1 is usually the target. First turn off reverb and FXloop, if it is still present, try this to narrow down the culprit: If you can get your hands on V1, remove it and turn on the amp. If you still hear the pops, turn off the amp and put the tube back into V1. Then remove V3 and power back up. If you still hear pops and such, do the same with V7. (Note with the preamp tubes removed there will be no signal path from the input to the speaker, we are just trying to identify where in the amp stages the noise is coming from. V3 is basically the final gain stage before the EQ and FX loop.

You could just pop in a new tube into V1 and if no change move to the next position with the new tube until you cannot hear the noise. Tube removal also works (note that it is okay to run the amp with a missing preamp tube, may not be practical but will help you find the issue.

You can also do the same thing with the power tubes, remove one, power up, no guitar signal for this test, also since half of the output stage will become unbalanced do not run it too long with a power tube missing.

If you use 90W mode, you can remove the Rectifier and see if the noise goes away. Rectifier is always active as it parallels the silicon diode and may contribute to noises (usually loud static like noises similar to turning on and off a light on the same electrical circuit the amp is plugged into.)

 

[lj678]

Hi Bandit2013,

Thanks for the informative response, it finally gave me hope again after avoiding eye contact with my Mark V for the past two weeks! :roll:

First I tried removing the rectifier tube but the noise was still present after I had turned the standby switch to on. After that I put the rectifier back in it's socket and pulled out a power tube to get access to the V1 preamp and removed that from the socket. Before powering back on I placed the power tube back in that I had removed previously and powered up. The noise was still there but I had to bring the master on the channel up considerably higher to hear it. The scratching was happening but less frequently and quieter.

Its quite a time consuming process as I have to wait for the power tubes to cool off before I can pull them out and get access to the preamps behind them because I still have the amp inside the chassis.

Moving onto V3, did the same process as I did with V1 and it reacted almost identical. The noise was happening only once (not in multiple bursts), roughly every 5-10 seconds and very quietly, I had to bring the master cranked to around 12 o'clock(usually it can still be heard with the volume rolled entirely off but of course gets louder as I bring the volume up.

After removing V7 it was completely different, no sound at all (no scratching or popping, finally :lol: ). Even when cranking the volume you would expect to hear a little bit of fuzz on a high gain channel which would increase with the volume but this wasn't the case here. I have a spare mesa 12AX7 which come with the amp when purchased (for all I know it could be a dud) but I put that into V7 and powered back up and the scratching popping is there again.

For the whole process nothing was plugged into the input, always using variac power(power switch down) 90w on channel 3 with reverb rolled off on all channels and FX loop bypassed.

Appreciate all the help you guys are giving as I really can't afford to take this to get looked at any time soon.
What should I do next? buy another preamp and see if that resolves the issue when in V7? Maybe try some contact cleaner on the tube sockets?
i'll try removing the power tubes one at a time tomorrow and see what happens.

 

[bandit2013]

V7 is the last tube in the sequence of stages in the preamp circuit. It is the Phase inverter tube and when removed all noise from the preamp will not be present to drive the power tubes.

one trick to determine if the PI or V7 is an issue, remove all the tubes except V7 (you will need the power tubes and rectifier tube installed.) if you hear the same noise that would narrow down to V7 or a power tube.

Another trick if you do not want to remove tubes, with all the tubes intact. Insert a cable into the send jack but do not use it. A short one will do, plug in another cable into the return (this one can be used with your guitar if you wish) FX loop must be set to active and select the FX loop with the rotary control to the channel that is active or to all. This will bypass the entire preamp on all channels except for V6 and V7. Note that the presence controls should still work for each channel (if you change channels that is). IF you do not get the snap crackle pop you can at least rule out V7 and power section and the look more into the lower number tubes. Note that V2, only half is used. You can pull that out and use it to substitute for another tube as you may have more than one preamp tube contributing to the noise.

on channel 3, the tubes in sequence how they are used (with the FX loop in hard bypass) V1A ->V1B -> V5A-> V4B->V3A->V6A->V7ab to power tubes. Removing V1 eliminates it contribution of the noise, if it gets reduced that may be partly a cause. If it changed, put a new tube in V1 and use V2 as a substitute for the next tube you think may be causing issue. V3 would be the next bet if the all channels are affected (with the reverb turned off). You can move the V3 tube to the V2 position if needed. Not sure what else can be done here. At least you ruled out the power tubes by removing V7 and the noise went away.

 

[lj678]

Ok I'm hearing the noise again with all preamps removed except for V7 now (the scratching sounds different to the previous noise though also I can't adjust it with the channel 3 master volume), so this must mean that its an issue with the power tubes or the phase inverter?

 

[bandit2013]

I apologize for the diagnosis routine, I had assumed you had just replaced the power tubes.... and that the preamp tubes may still be in good condition. Well the preamp removal method can work out most of the time. However I went back into this post on the early comments and did not notice the recording you made until this morning. That sounds more like the Rectifier tube causing the problem. Also if you are running the EL34 tubes at full power and not variac power (the EL34 will have a shorter life span since the plate voltage is a bit high for EL34 tubes). Awesome playing by the way despite the static pops. It does remind me of a preamp tube issue but it also sounds like it is contributed by the Rectifier tube.

You can return all of the preamp tubes back into the amp as I doubt they are contributing to the problem. The popping noise is getting louder or more dominant because the noise level in the preamp circuits is causing more current flow in the power tubes. With V7 removed, the power tubes are at idle and may not make any noise as there is no current flow other than bias current. It is the change in current flow cause by signal that is resulting in the pops. One rule of thumb if you have reached the end of life on one of the power tubes and you are due for replacement, always change the Rectifier tube at the same time. The pops you are hearing is contributed by the Rectifier tube. I am sure if you rotated the head around and watch the power tubes in the dark you will see lighting in the Rectifier tube. I have had this problem a few times but was generally contributed by the power tubes reaching end of life. The discharge in the Rectifier tube can get severe but it is also preventing the silicon diodes from sudden death since the Rectifier tube is running parallel to the diodes and is always in the circuit. You may also be more at risk of loosing a screen resistor on one of the inner pair of power tubes. I had this happen already. You would know it if it does occur as the resistor smells really bad when it fails (usually associated with lots of smoke before it blows the fuse), amp will not work after that until the resistor(s) get replaced.

Sounds like you are in need of a new power tubes and Rectifier, may as well update your preamp tubes if they have been in the amp since the day you brought it home.

 

[lj678]

I'm still waiting for the new rectifier tube to be delivered, i'll let you know what the outcome is.

Surely I wouldn't need new power tubes? These Electro Harmonix el34s have had less than an hour play time, only in use while I was trying to diagnose the issue

 

[bandit2013]

Good luck with that.... the Mesa 5U4GB is also the same as the EHX 5U4GB. I have used both in the Mark V. A diode rectifier is just that, it will not affect the tone of the amp but may affect the character or sag you get using the 45W mode on CH1 and CH2.

Here is a trick.....it does work too. If you are running 90W power mode, the silicon diodes are always active and they are in parallel to the tube rectifier. You can run the amp without the Rectifier for diagnosis purpose as it is insufficient to supply power to the 90W mode. There may be some added benefit of having it in the circuit at all times since it is in parallel so the current path is present though both the Rectifier diodes as well as the tube Rectifier. If you get the same static sound with the Rectifier removed it may not be the root cause of the problem.

If the new rectifier tube is not the solution.... and considering the amp is out of warranty. I would call Mesa Customer service for advice after you have ruled out it is not tube related. There may be something else causing the issue.