New tubes, tone still changes randomly

[Tone1026]

http://www.mouser.com/ProductDetail...=sGAEpiMZZMtbXrIkmrvidFNEWMAwu8Y/KT4Nv/nTBcg=

This resistor work?

Use a metal film, flame proof type. You could probably go up to a 3W size. The resistor you selected is wire wound and has a lower voltage rating. I did not see any maximum operating voltage listed except for the ohms law equation. Metal oxide type would be better. Also the one listed below is rated for high voltage. 1k ohm, 2w, 1%, flame proof, has lower inductance than the wire wound type. Consider the maximum voltage potential.


http://www.mouser.com/ProductDetail...GAEpiMZZMvmQ%2bOLa8n/M6RIedYzYbs9Y9lYFwOm3wo=

Thanks. I wonder if running those el34 in diode mode ignorantly was what cooked that tube...

 

[shimmilou]

Please forgive my error, it's hard to follow the trail on multiple threads. I'll delete that part of my previous post.

Yes, clean off all carbon residue, from all parts. Check the other resistors in the same way that I explained before, start with a visual, also check the ohms value with a meter. Yes, sometimes more than one resistor can be damaged. Whatever caused this damage, such as a shorted tube, could have also caused more damage. I sometimes see the same damage done to both tubes right next to each other. The two tubes on the right side, handle half of the output signal (push), and the two tubes on the left side handle the other half (pull), giving you the push-pull of a tube amp. Using the amp in this crippled shape would be a push-pull, putting a little more strain on the one tube working by itself handling half of the output, while two tubes are handling the other half of the output.

That resistor in your link from mouser, looks very similar and might work, but it is only a 500 Volt dielectric strength, which is close to the voltage that it will see in the amp. But a search for "Dale RS-2" brings up a 2.5 watt or 3 watt resistor, with a 1000 Volt dielectric strength, and if in doubt, I would probably err on the side of a higher watt and higher voltage resistor. Maybe even getting four and changing the other three screen grid resistors also. Maybe this one:

http://www.mouser.com/ProductDetail...=sGAEpiMZZMtbXrIkmrvidNrdKKeO5KTNorcjj3vRJsc=

Measure the existing resistor diameter and length and compare to the specs on Mouser site. There is quite a difference in the diameter between the 2 watt, and the 2.5 watt or 3 watt resistors. All of the Mesa schematics that I have looked at show only 2 watt resistors, so the one that you found might be just fine.

Previewing my post, I saw that bandit2013 linked to a suitable resistor also. I can't disagree with his choice either, even though it is physically much larger in size than any of the previous resistors.

 

[Tone1026]

Please forgive my error, it's hard to follow the trail on multiple threads. I'll delete that part of my previous post.

Yes, clean off all carbon residue, from all parts. Check the other resistors in the same way that I explained before, start with a visual, also check the ohms value with a meter. Yes, sometimes more than one resistor can be damaged. Whatever caused this damage, such as a shorted tube, could have also caused more damage. I sometimes see the same damage done to both tubes right next to each other. The two tubes on the right side, handle half of the output signal (push), and the two tubes on the left side handle the other half (pull), giving you the push-pull of a tube amp. Using the amp in this crippled shape would be a push-pull, putting a little more strain on the one tube working by itself handling half of the output, while two tubes are handling the other half of the output.

That resistor in your link from mouser, looks very similar and might work, but it is only a 500 Volt dielectric strength, which is close to the voltage that it will see in the amp. But a search for "Dale RS-2" brings up a 2.5 watt or 3 watt resistor, with a 1000 Volt dielectric strength, and if in doubt, I would probably err on the side of a higher watt and higher voltage resistor. Maybe even getting four and changing the other three screen grid resistors also. Maybe this one:

http://www.mouser.com/ProductDetail...=sGAEpiMZZMtbXrIkmrvidNrdKKeO5KTNorcjj3vRJsc=

Measure the existing resistor diameter and length and compare to the specs on Mouser site. There is quite a difference in the diameter between the 2 watt, and the 2.5 watt or 3 watt resistors. All of the Mesa schematics that I have looked at show only 2 watt resistors, so the one that you found might be just fine.

Previewing my post, I saw that bandit2013 linked to a suitable resistor also. I can't disagree with his choice either, even though it is physically much larger in size than any of the previous resistors.

No problem. sorry for not being more organized with how i posted the stuff..
I appreciate the time you have spent and the help you have been

 

[Tone1026]

So could that burnt resistor have something to do with why my direct tone is well, how should i say... LAME? no gain saturation unless the gain is cranked, even then not so hot... 12 oclock to 3 oclock on the gain dial is white stripes distortion...

 

[shimmilou]

That burnt resistor keeps that output tube from working, so it will affect tone/volume of the amp.

 

[bandit2013]

I never cared much for mouser. I usually use digikey.

Tone1026, have you seen any reference to BOM on the schematics for mesa's. Getting the correct part would be best than a substitute.

The only time I ever saw cracks like that on a component was due to overvoltage. Typically on monolithic bridge rectifiers. What ever is causing the transient spike or arc probably damaged other components. More than likely the arc was caused by the OT. It is probable the damage was done before you got the amp (assuming you are not the original owner). No load on the OT will cause high voltage to be generated on the primary in excess of 10kV (considering the arc length between the pins). It is best not to turn you amp into a Jacob's Ladder (doubt that would ever happen).

 

[Tone1026]

I never cared much for mouser. I usually use digikey.

Tone1026, have you seen any reference to BOM on the schematics for mesa's. Getting the correct part would be best than a substitute.

The only time I ever saw cracks like that on a component was due to overvoltage. Typically on monolithic bridge rectifiers. What ever is causing the transient spike or arc probably damaged other components. More than likely the arc was caused by the OT. It is probable the damage was done before you got the amp (assuming you are not the original owner). No load on the OT will cause high voltage to be generated on the primary in excess of 10kV (considering the arc length between the pins). It is best not to turn you amp into a Jacob's Ladder (doubt that would ever happen).

Well to be honest i will more than likely pay the 35$ bench fee to have the tech I spoke with do the work. My time is worth more than that. The local tech i spoke with said that he has the right resistor. I will verify that it is at least 2 w 1k 1%.

What is the OT?
I bought the amp a few months ago. I had a moment of stupidity in running the amp in diode mode w/ el34's and a stack of papers sitting on the vent. The amp was also sitting close to the wall. I heard a swoshing sound, like that of a flanger, and shut the amp off. I am not sure if the tube/resistor failed then, or if the problem already existed.

What should i ask the tech to look for?

I have decided to not use it till its fixed. I saw no other visibly bad components, but it would have to be obvious for me to catch it..

What do you mean by turning the amp into a "Jacobs Ladder"?

 

[bandit2013]

OT is abreviation for Output Transformer.

Jacobs ladder, sorry, most would not get the reference. Jacobs ladder is an arc generator based on a tesla coil. It is shaped like two old tv antennea in the form of a V. The arc will dance from the bottom to the top of the v shaped wires. It is usually seen in old mad sci-fi movies like Frankenstein's monster or similar.

$35 is not bad. Will the tech do a full check on everything? and is it covered for any period of time after the repair?

 

[Tone1026]

$35.00 was just to fix the resistor, he's going to go through and look at everything he said for $45. I think that's his hourly bench rate. Als diner out of Jackson. I would only expect him to stand behind what he fixed.

 

[Tone1026]

Well I got the resistor replaced. Noticed quite an improvement in output for sure, however last night, i noticed the switch in tone again. I would say it more frequently is starting bright/thin, then switching to a thicker/darker tone, sometimes I can make it change to the darker tone by changing channels modes back and forth, sometimes just with extended play. Happened last night at low volume. I dont know if it is channel specific yet. right now it is happening on the orange channel when in the orange to modern, clean setting. I wondered if it is something that is happening when it is warming up... The tech said all the tubes (JJ 6l6) tested exactly the same. he said they are fine, but they are cold tubes (they measued "14") I can get more info from him if needed. He also said all the resistors checked out fine.

I am pretty sure that it is not related to the pedal board/ chords/ guitar as i have never noticed this problem till i bought this amp. But it is possible i guess.
The amp has been plugged into a 10 strip, which i changed last night. Maybe that will help... :?

If it is a warming up issue it should just be a switch to thicker darker, not the other way around right?

 

[Tone1026]

yup just happened after playing at low vol. for 10 min. no increase in bass just a substantial drop in high end...it was like a switch got flipped no increase in volume..

 

[shimmilou]

...I am pretty sure that it is not related to the pedal board/ chords/ guitar as i have never noticed this problem till i bought this amp. But it is possible i guess...

At this point, you should isolate the amp, unplug all pedals/effects and just have guitar straight into amp, nothing in the loop. This is essential for troubleshooting. If you still notice the tone change using only guitar and amp, first thing to do would be to try another instrument cable and another guitar to further eliminate all possibilities except the amp.

 

[Tone1026]

.

 

[Tone1026]

From what ive found it is reletive to the Orange channel. it can be triggered by switching modes either clean - dist and back, or orange to modern to normal and back. Any amp related suggestions. I have run the guitar direct to red, havent heard the switch, run also in orange direct, yet to hear the switch, The switch in tone is in the clean channel. again a pretty dramatic cut in high end.. Thoughts?

 

[Tone1026]

I think i am going to post this issue under the rectifier series area as i see it less as a tube issue, it is obviously triggered by the clean gain switch, though it changes over time aswell.. Should i post a link to this thread aswell? It may be 2 channel specific problem.

 

[shimmilou]

You already have your problem spread out over several threads, which is confusing enough, and it would just add to the confusion to keep starting new threads over and over. :roll:

So, do you still have guitar plugged straight into the amp, with nothing else plugged into the amp? It seemed that your deleted post above indicated that your problem was not with the amp. Since you have paid someone to look at your problem and he didn't quite fix it as indicated, I would call that person back and see what's up, or take it to someone that can fix it.

Is there really anything that you can do, such as checking all of your components thoroughly with a meter, checking supply voltages and checking your tubes? Do you have schematics? At this point you are just shooting in the dark with no real plan and seemingly very limited in troubleshooting ability. If you had to take it to a shop to replace a resistor, I am beginning to believe that there isn't anything that you could do yourself anyway. :|

 

[Tone1026]

You already have your problem spread out over several threads, which is confusing enough, and it would just add to the confusion to keep starting new threads over and over. :roll:

So, do you still have guitar plugged straight into the amp, with nothing else plugged into the amp? It seemed that your deleted post above indicated that your problem was not with the amp. Since you have paid someone to look at your problem and he didn't quite fix it as indicated, I would call that person back and see what's up, or take it to someone that can fix it.

Is there really anything that you can do, such as checking all of your components thoroughly with a meter, checking supply voltages and checking your tubes? Do you have schematics? At this point you are just shooting in the dark with no real plan and seemingly very limited in troubleshooting ability. If you had to take it to a shop to replace a resistor, I am beginning to believe that there isn't anything that you could do yourself anyway. :|

Ok. Well i paid him to change resistor, and check the other resistors/tubes. Assumed that would fix the problem, and it didn't as i stated above. I have plugged in direct red and orange gain mode and haven't heard it. I have only heard it in clean orange as i also stated above. Hard to hear that kind of change in clean. So running through the processor i notice it at the moment i switch modes in the back of the amp. I'm no certified mesa tech, but i would say its not the processor as it does it right when i switch channels/modes. Also NEVER heard that on ANYTHING ive run that processor through.
I guess if someone on hear reading this is familiar with the 2ch. Tr and has any suggestions to help narrow it down i would appreciate the input. Maybe something to do with the channel cloning?

 

[Tone1026]

I know it is normal for some pop when switching channels, esp. when modes are different. The popping heard on my amp when switching from clean orange modern to anything else is substantial.. like a surging type pop.. Which triggers the change in tone consistantly. once it switches, its not quick to switch back. Usually doesn't after the initial switch..

 

[Tone1026]

Well i changed the treble setting turning it down on the orange channel. Which adds all sorts of punch. I think maybe the processor was sending to bright/ compressed a signal or something because of the pre amp?? Anyway I havent heard the switch since i changed the treble setting.

 

[Tone1026]

Nm still does it...