Bought an attenuator today

[1neeto]

And I think it just killed my power amp tubes. I was playing with it, and set it to max and tried to push the volume to see if my amp would start clipping. The volume on the master was at around 6, and it had this sweet tone that was right at the limit, so I stomp on my distortion pedal, and tube screamer, and about 5 seconds later I hear the amp just fade into nothing. I panic, and flip the standby switch, and turn the attenuator to 0. Turned off the amp and waited about 10 minutes. Then went through the sequence of warming up the tubes, guitar volume in zero, I then flip the standby to on, and gradually raise the volume on my guitar. With the master at 6, I expected quite the loud sound this amp makes at that volume. I usually can’t go past 3 without having an angry wife knocking on my door. But this time, the amp sounded as if the attenuator was still active. I look to make sure it’s on zero, and it is. I then remove it and connect the speaker to the amp, and still low volume. The amp still has good tone, but I lost a good 30% or so of overall volume.

The tubes light up nice and orange, the pre amp tubes are harder to see, so I’ll remove some covers tomorrow and have a closer look and give them some love taps. This is a Mesa Subway Rocket, and the tubes say Mesa so, it’s possible they’re the factory tubes from the 90’s. Should I replace just the power tubes since the volume loss is in all channels? Or could I be looking at something more serious?

Here’s the attenuator I used. I looked it up, and it’s supposed to be a good one. It was quite cheap at GC used gear pile so couldn’t pass it up.


Sent from my iPhone using Tapatalk

[JamesPaul]

Since you added the attenuator in, the first thing I would try is spraying some Deoxit on the plugs, then plug/unplug them from the jacks a few times. I have not experienced the dirt/oxidation on speaker jacks causing a volume loss, but that does not mean it cannot happen. Plus it is an inexpensive fix if it resolves it.

If you have another amp you can test the speaker on, do that and rule out a speaker issue.

If not, next I would try replacing the power tubes. They are EL84 - correct? Those are not known for a long lifespan. I also replace my phase inverter tube when replacing my power tubes.

If the overall tone has not changed, only the volume loss, the preamp tubes should be fine.

You had a load on it the entire time, so the output transformer should be fine.

Electronic components can always degrade or fail. If the cleaning or tubes do not resolve it you probably need to have it looked at for a component in the power amp starting to go out. Bias going cold, plate voltage dropping, grid resistor issues, etc. type of stuff.

Edit: While you have the Deoxit out, might as well clean all the jacks, just in case it was a coincidence of some other jack being dirty.

[jeremy]

the z brake is a fine attenuator. an attenuator wont hurt your amp by itself, but running the amp hot and slamming it with pedals will push it to the limit so if something was getting tired or had some issue, that will pop it. i kinda doubt its the speaker since you were running sending a bunch of the signal to the attenuator but doesnt hurt to check since its easy if you have another speaker layin around

[1neeto]

the z brake is a fine attenuator. an attenuator wont hurt your amp by itself, but running the amp hot and slamming it with pedals will push it to the limit so if something was getting tired or had some issue, that will pop it. i kinda doubt its the speaker since you were running sending a bunch of the signal to the attenuator but doesnt hurt to check since its easy if you have another speaker layin around

That’s what I’m thinking. I bet the tubes are just tired to begin with. I’ve been using this amp at bedroom volume which is 2.5, maybe 3. With the attenuator maxed out I had it twice as high at around 6 and then slammed it with the distortion pedal and ts, and maybe that’s all the old tubes could handle. The good news is that the tone is not lost, and the volume loss is even on all 3 channels so I think the pre amp tubes are fine.

Since you added the attenuator in, the first thing I would try is spraying some Deoxit on the plugs, then plug/unplug them from the jacks a few times. I have not experienced the dirt/oxidation on speaker jacks causing a volume loss, but that does not mean it cannot happen. Plus it is an inexpensive fix if it resolves it.

If you have another amp you can test the speaker on, do that and rule out a speaker issue.

If not, next I would try replacing the power tubes. They are EL84 - correct? Those are not known for a long lifespan. I also replace my phase inverter tube when replacing my power tubes.

If the overall tone has not changed, only the volume loss, the preamp tubes should be fine.

You had a load on it the entire time, so the output transformer should be fine.

Electronic components can always degrade or fail. If the cleaning or tubes do not resolve it you probably need to have it looked at for a component in the power amp starting to go out. Bias going cold, plate voltage dropping, grid resistor issues, etc. type of stuff.

Edit: While you have the Deoxit out, might as well clean all the jacks, just in case it was a coincidence of some other jack being dirty.

I don’t have deoxit, but I have a can of QD electronic cleaner, which is what I use with success if I have crackly pots. I understand deoxit leaves a protective layer, instead of completely evaporate so I might give that a shot. I’m gonna also try and jump the effects loop jacks, since I’ve noticed one of my chorus and delay pedals pop really loud when I stomp on it, and I read that sometimes dirty loop jacks can create a volume loss situation.

The power tubes are EL84, and pre amp tubes are 12AX7’s. They’re all Mesa brand so maybe they’re the factory ones, Which would be quite impressive.

Thanks for the feedback guys.


Sent from my iPhone using Tapatalk

[JamesPaul]

That’s what I’m thinking. I bet the tubes are just tired to begin with. I’ve been using this amp at bedroom volume which is 2.5, maybe 3. With the attenuator maxed out I had it twice as high at around 6 and then slammed it with the distortion pedal and ts, and maybe that’s all the old tubes could handle. The good news is that the tone is not lost, and the volume loss is even on all 3 channels so I think the pre amp tubes are fine.


I don’t have deoxit, but I have a can of QD electronic cleaner, which is what I use with success if I have crackly pots. I understand deoxit leaves a protective layer, instead of completely evaporate so I might give that a shot. I’m gonna also try and jump the effects loop jacks, since I’ve noticed one of my chorus and delay pedals pop really loud when I stomp on it, and I read that sometimes dirty loop jacks can create a volume loss situation.

The power tubes are EL84, and pre amp tubes are 12AX7’s. They’re all Mesa brand so maybe they’re the factory ones, Which would be quite impressive.

Thanks for the feedback guys.


Sent from my iPhone using Tapatalk

I have several amps with EL84 power tubes. When they were being heavily used (daily practice, weekly rehearsal, gig or two monthly and transported in between) I never pushed a set of EL84s much more than one year. Even now that they have been getting minimal use since ~2010, none of my EL84s are more than six years old. If you have been using your set since the '90s, they are likely due for a change to get the optimal tone out of your amp. Even if there has not been a failure.

The phase inverter 12AX7 is likely due as well.

The preamp 12AX7s, especially if you are not moving the amp around a lot, will usually last until they go harmonic or fail.

Your QD cleaner should be fine on the jacks.

[beaubrummels]

I would suspect the output transformer possibly. Amps with an attenuator can be hard on the output transformer. You said all the tubes look normal. If you are getting partial volume, I would expect some of the tubes to not light up, or glow brighter/different color, like they are burning up.

Is that speaker cable? It doesn't look like speaker cable. That would be a problem.

[1neeto]

I would suspect the output transformer possibly. Amps with an attenuator can be hard on the output transformer. You said all the tubes look normal. If you are getting partial volume, I would expect some of the tubes to not light up, or glow brighter/different color, like they are burning up.

Is that speaker cable? It doesn't look like speaker cable. That would be a problem.

That jack on the pic is the attenuator input plugged into the output just so I don’t have the lead dangling around. That pic is when I just bought the thing. I really hope it’s just something simple like a tube or dirty jacks.

I have several amps with EL84 power tubes. When they were being heavily used (daily practice, weekly rehearsal, gig or two monthly and transported in between) I never pushed a set of EL84s much more than one year. Even now that they have been getting minimal use since ~2010, none of my EL84s are more than six years old. If you have been using your set since the '90s, they are likely due for a change to get the optimal tone out of your amp. Even if there has not been a failure.

The phase inverter 12AX7 is likely due as well.

The preamp 12AX7s, especially if you are not moving the amp around a lot, will usually last until they go harmonic or fail.

Your QD cleaner should be fine on the jacks.

This amp I just got a few weeks ago. I have no idea of its history, other than the previous owner had it for a few years and never changed the tubes. I’m assuming the tubes might be factory because all of them say Mesa. I find it highly unlikely that someone would replace them all with Mesa tubes but I could be wrong. I’m probably wrong. Lol!


Sent from my iPhone using Tapatalk

[JMP/HBE]

They always sound great right before they croak.
Did you correctly match speaker load impedance ?

[1neeto]

They always sound great right before they croak.
Did you correctly match speaker load impedance ?

Speaker is 8ohms and I used the 8ohms jack. The attenuator does 8ohms.


Sent from my iPhone using Tapatalk

[JamesPaul]

I have never seen an output transformer fail when using an attenuator. Also I would expect Mesa to use a relatively robust, if not overrated, output transformer. That you only lost volume, not a complete loss of sound, would indicate the output transformer did not completely blow.

Mesa does not manufacture tubes, but they likely get specific tubes from someone and relabel them. Maybe from Groove Tubes, who does not manufacture either, but they used to have some stringent testing and matching procedures for what they resell. I could see Mesa owners getting replacement tubes from Mesa.

I never mismatch impedances. I find no tonal advantage and it does pose a risk to the output transformer or power amp circuit. Unfortunately I know plenty of people who do. Still I would be surprised if a one tap off would damage the output transformer, unless Mesa is using a much less robust output transformer than I am expecting. An amp on 4 ohms and a 16 ohm attenuator/speaker load would be a more likely suspect of causing an output transformer issue.

If not dirty jacks, I am still thinking power tubes are the most likely cause given the observed symptoms. Next most likely is some component degrading in the power amp circuit.

[1neeto]

Cleaned the jacks to no avail. Amp still sounds great, so it doesn’t really bother much as much anymore. Worst that can happen is for a tube to completely fail. Now shopping for tubes is a first for me. I’m sure the choices are endless.


Sent from my iPhone using Tapatalk

[JamesPaul]

You will have options, but they should not be too intimidating. There are a couple of topics in The Vault which may help.

EL84
https://forum.seymourduncan.com/foru.../155930-el-84s

12AX7

https://forum.seymourduncan.com/foru...ootout-results

Most tube selling sites will also have reviews.

If there are Mesa sites, they will probably have reviews also.

Edit: I just searched and Eurotubes is showing the Subway Rocket is self biased.

https://www.eurotubes.com/store/pc/Mesa-Boogie-Subway-Rocket-Subway-Rocket-Reverb-c189.htm

[1neeto]

You will have options, but they should not be too intimidating. There are a couple of topics in The Vault which may help.

EL84
https://forum.seymourduncan.com/foru.../155930-el-84s

12AX7

https://forum.seymourduncan.com/foru...ootout-results

Most tube selling sites will also have reviews.

If there are Mesa sites, they will probably have reviews also.

Edit: I just searched and Eurotubes is showing the Subway Rocket is self biased.

https://www.eurotubes.com/store/pc/M...everb-c189.htm

Wow did I read that right? $100 buys me a full tube kit?


Sent from my iPhone using Tapatalk

[JamesPaul]

Yes, that is for their retube kits. They are actually charging more than you could buy those brand and type of tubes for, but the extra covers their testing, matching and grading work so you can specify breakup.

[1neeto]

Yes, that is for their retube kits. They are actually charging more than you could buy those brand and type of tubes for, but the extra covers their testing, matching and grading work so you can specify breakup.

Yeah that’s what I meant that they match them and all. Also the self biased means that just swap the tubes and that’s it? This is completely new stuff to me. Always played with solid state or modeling amps.


Sent from my iPhone using Tapatalk