Mesa MarkV / Saturation 'mod'

bandit2013 said:

Hey, no problem, how else can one figure this thing out without a full schematic. I believe your issue is related to the ribbon cable you disconnected when you cut the leg to the cap. The ribbon cables also carry signals too. I have not decoded the other ribbon cables yet but at least the mute thing may not be the problem.

I have gone back to 12AX7s then back to 12AT7 in V4, now have both in V4 and V6. The tube swap is a good fix for the ice pick.

I think I have been the one hogging the thread. sorry. :roll:

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No apologies Bandit. You have took APEMAN'S great thread he started here and helped it evolve into the behemoth that it has become. You've given some great advice and insight into the reasons behind the effectiveness of the AT7 mod in both V4 and V6. And you've helped me with my problem along the way. Thanks to you I now have AT7's in V4 and V6 in my V and when it was working it sounded heavenly good. Looking forward to getting it fixed, missing it now.

Wayno said:

bandit2013 said:

Hey, no problem, how else can one figure this thing out without a full schematic. I believe your issue is related to the ribbon cable you disconnected when you cut the leg to the cap. The ribbon cables also carry signals too. I have not decoded the other ribbon cables yet but at least the mute thing may not be the problem.

I have gone back to 12AX7s then back to 12AT7 in V4, now have both in V4 and V6. The tube swap is a good fix for the ice pick.

I think I have been the one hogging the thread. sorry. :roll:

Click to expand...

No apologies Bandit. You have took Bandits great thread he started here and helped it evolve into the behemoth that it has become. You've given some great advice and insight into the reasons behind the effectiveness of the AT7 mod in both V4 and V6. And you've helped me with my problem along the way. Thanks to you I now have AT7's in V4 and V6 in my V and when it was working it sounded heavenly good. Looking forward to getting it fixed, missing it now.

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You know how it is with/what they they say about absence.

Those 1st chords you play when it returns will be be most awesome experience you've ever had.
Glad to hear progress is being made. Steps in the right direction for sure.

I was thinking about re-biasing the V4B circuit. Change in the cathode resistance and anode resistance to get a closer gain using a 12AX7 as I am getting with the original using the 12AT7. Nah, that is too much effort and work required to get very little in return. Tube swap is the best solution. I do not need the amp to sound like the JP-2C as I have one of those. The 12AT7 does a good job at getting close enough. Then there are the other preamp tubes you can change to fine tune the tone. I am happy with the Mark V where it is at. Yep it has its unique tone to it, not as ice pick bright any more and the change in speakers made a huge difference in my books. Running the Mark V combo with the OTR speaker and a 112 open back extension cab with the same speaker in it.

Are you guys using pentode or triode with this "mod"? I've been using triode cause that's what the manual says to use if you want a more authentic Iic+ sound. But today I read an article about the guitarist from slipknot talking about how much he loves the jp-2c and about Hetfield running the iic+ into a Marshall powerm amp. In his words he said Hetfield did because the iic+ had no balls because it was wired triode. Anyway I flicked the switch and bam, more balls :twisted:

Edit, I may have the pentode/triode thing arse about face.

barryswanson said:

Are you guys using pentode or triode with this "mod"? I've been using triode cause that's what the manual says to use if you want a more authentic Iic+ sound. But today I read an article about the guitarist from slipknot talking about how much he loves the jp-2c and about Hetfield running the iic+ into a Marshall powerm amp. In his words he said Hetfield did because the iic+ had no balls because it was wired triode. Anyway I flicked the switch and bam, more balls :twisted:

Edit, I may have the pentode/triode thing arse about face.

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Thats probably just his preference.

Its not about balls tonally, its an output type thing. The more scooped darker nature of Triode and the feel are more vintage Metallica I'd say, when not slaved through a Marshall, for my money, but the overall volume is less than Pentode, and the feel is different in Pentode..... I heard from a interview with Flemming Rassmussen that slaving into the Marshall its was to bring more dirty/heavy to the tone, as he felt the IIc+ was too clean/civilised.

Oh yeah, that switch on the back. I have left it in Pentode and forgot it was there..... I have tried both, depends on what I am after. For more clarity in note definition triode seems to be ideal but for full on grunt and punch the pentode is it.

bandit2013 said:

Oh yeah, that switch on the back. I have left it in Pentode and forgot it was there..... I have tried both, depends on what I am after. For more clarity in note definition triode seems to be ideal but for full on grunt and punch the pentode is it.

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This thread sure has a lot of split ends. haha

I run triode in the band as pentode seems to cause a little “mud” with the bass player at times. It seems the triode blends better. This is with IIc+ and IV modes, 45 and 90W, mostly IIc+/45.

In 10W mode, all channel 3 voices are wired pentode (switch has no effect).

Markageddon said:

barryswanson said:

Are you guys using pentode or triode with this "mod"? I've been using triode cause that's what the manual says to use if you want a more authentic Iic+ sound. But today I read an article about the guitarist from slipknot talking about how much he loves the jp-2c and about Hetfield running the iic+ into a Marshall powerm amp. In his words he said Hetfield did because the iic+ had no balls because it was wired triode. Anyway I flicked the switch and bam, more balls :twisted:

Edit, I may have the pentode/triode thing arse about face.

Click to expand...

Thats probably just his preference.

Its not about balls tonally, its an output type thing. The more scooped darker nature of Triode and the feel are more vintage Metallica I'd say, when not slaved through a Marshall, for my money, but the overall volume is less than Pentode, and the feel is different in Pentode..... I heard from a interview with Flemming Rassmussen that slaving into the Marshall its was to bring more dirty/heavy to the tone, as he felt the IIc+ was too clean/civilised.

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This would make sense, simulclass adds back in the harmonic present in class A that gets nullified in class AB according to mesa, therefore a smoother tone. Flemming probably preferred the more raw sound of class AB so he slaved to a Marshall to achieve that. Either way, the tone on Master of Puppets is intense so mission accomplished I'd say. Doesn't the Mark V manual say something about all simulcass iiC+'s bring wired in triode? I'd also hazard a guess that the marshall amp they used was Pentode?

Personally I have always prefered Triode on my Mark V as I find Pentode feels a bit stiff, that will probably change once I get it back from repair though. Now I have V4 and V6 as AT7's again I might like the definate extra balls/volume that Pentode adds. We'll see.

Hey, Keep us informed when you get your amp back. Would like to know what was up with that and why It went silent after you did the capacitor mod. I feel bad suggesting it but more than likely it was coincidental if it is the same component on the grid to cathode on V4B. Also if your repair guy can account for its actual purpose (other than to reduce high frequency oscillations as well as making creating a small signal low pass filter and compounding the Miller capacitance).

bandit2013 said:

Hey, Keep us informed when you get your amp back. Would like to know what was up with that and why It went silent after you did the capacitor mod. I feel bad suggesting it but more than likely it was coincidental if it is the same component on the grid to cathode on V4B. Also if your repair guy can account for its actual purpose (other than to reduce high frequency oscillations as well as making creating a small signal low pass filter and compounding the Miller capacitance).

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Will defo let you know, don't feel bad about suggesting the cap mod. I chose to try it and that wasn't the reason i had the failure. I forgot to reconnect the ribbon cable. It was all my choice. My fault for not paying enough attention, which is a silly thing to do safety wise what with the voltages involved, let alone the value of the amp itself. Will definately find out his opinion on the cap and its purpose but im sure your right with that regard. Hopefully should all make sense when he finds the faulty component.

Any news to report, Wayno..?

Just picked it up today. No joy unfortunately. He thinks it is one of the Jfets but he can't get the part and he can't get the right schematic for it, or the one he's got dosen't seem to match the layout of the amp. He said the English authorised service centre weren't very much help to him at all so I think I'm going to have to take it to them direct. Only they're in Scotland apparently, cost a fortune to post it safely up to there so I'm gonna have to drive it up myself. The wife joked about having a holiday up there at the same time, might not be a bad idea to be honest.

I'm gutted, got a very expensive door stop at the moment. Anyone know of an authorised service centre closer to Norfolk than Scotland that the tech might not have known about? Or anyone else who might be able to help? I'm a little surprised that the Jfet is that hard to get hold of? Thought they are a pretty generic component?

Wayno said:

Just picked it up today. No joy unfortunately. He thinks it is one of the Jfets but he can't get the part and he can't get the right schematic for it, or the one he's got dosen't seem to match the layout of the amp. He said the English authorised service centre weren't very much help to him at all so I think I'm going to have to take it to them direct. Only they're in Scotland apparently, cost a fortune to post it safely up to there so I'm gonna have to drive it up myself. The wife joked about having a holiday up there at the same time, might not be a bad idea to be honest.

I'm gutted, got a very expensive door stop at the moment. Anyone know of an authorised service centre closer to Norfolk than Scotland that the tech might not have known about? Or anyone else who might be able to help? I'm a little surprised that the Jfet is that hard to get hold of? Thought they are a pretty generic component?

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You should contact Westside DIRECTLY...

Westside Distribution

100, Fifty Pitches Road, Glasgow, G514EB

P: +44 0844 326 2000
F: +44 (0) 141 248 4813
http://quickfind.me/mesa

Authorized Boogie said:

Wayno said:

Just picked it up today. No joy unfortunately. He thinks it is one of the Jfets but he can't get the part and he can't get the right schematic for it, or the one he's got dosen't seem to match the layout of the amp. He said the English authorised service centre weren't very much help to him at all so I think I'm going to have to take it to them direct. Only they're in Scotland apparently, cost a fortune to post it safely up to there so I'm gonna have to drive it up myself. The wife joked about having a holiday up there at the same time, might not be a bad idea to be honest.

I'm gutted, got a very expensive door stop at the moment. Anyone know of an authorised service centre closer to Norfolk than Scotland that the tech might not have known about? Or anyone else who might be able to help? I'm a little surprised that the Jfet is that hard to get hold of? Thought they are a pretty generic component?

Click to expand...

You should contact Westside DIRECTLY...

Westside Distribution

100, Fifty Pitches Road, Glasgow, G514EB

P: +44 0844 326 2000
F: +44 (0) 141 248 4813
http://quickfind.me/mesa

Click to expand...

Thank you,

Really hoped there was one closer to home though. Courier services in England are notoriously crap to be frank, I should know I used to sub contract for them, and I really don't want to have to trust them with my Mark V. Not to mention that would cost a small fortune too only for them to lose it or damage it further. That leaves me with a good 12 hour round trip to get to Glasgow and back home, twice if I have to leave it with them ( more than likely ).

Wayno said:

Authorized Boogie said:

Wayno said:

Just picked it up today. No joy unfortunately. He thinks it is one of the Jfets but he can't get the part and he can't get the right schematic for it, or the one he's got dosen't seem to match the layout of the amp. He said the English authorised service centre weren't very much help to him at all so I think I'm going to have to take it to them direct. Only they're in Scotland apparently, cost a fortune to post it safely up to there so I'm gonna have to drive it up myself. The wife joked about having a holiday up there at the same time, might not be a bad idea to be honest.

I'm gutted, got a very expensive door stop at the moment. Anyone know of an authorised service centre closer to Norfolk than Scotland that the tech might not have known about? Or anyone else who might be able to help? I'm a little surprised that the Jfet is that hard to get hold of? Thought they are a pretty generic component?

Click to expand...

You should contact Westside DIRECTLY...

Westside Distribution

100, Fifty Pitches Road, Glasgow, G514EB

P: +44 0844 326 2000
F: +44 (0) 141 248 4813
http://quickfind.me/mesa

Click to expand...

Thank you,

Really hoped there was one closer to home though. Courier services in England are notoriously crap to be frank, I should know I used to sub contract for them, and I really don't want to have to trust them with my Mark V. Not to mention that would cost a small fortune too only for them to lose it or damage it further. That leaves me with a good 12 hour round trip to get to Glasgow and back home, twice if I have to leave it with them ( more than likely ).

Click to expand...

You've spoken with their Service Manager already? He typically can provide local authorized repair...Thanks

You should contact Westside DIRECTLY...

Westside Distribution

100, Fifty Pitches Road, Glasgow, G514EB

P: +44 0844 326 2000
F: +44 (0) 141 248 4813
http://quickfind.me/mesa[/quote]

Thank you,

Really hoped there was one closer to home though. Courier services in England are notoriously crap to be frank, I should know I used to sub contract for them, and I really don't want to have to trust them with my Mark V. Not to mention that would cost a small fortune too only for them to lose it or damage it further. That leaves me with a good 12 hour round trip to get to Glasgow and back home, twice if I have to leave it with them ( more than likely ).[/quote]

You've spoken with their Service Manager already? He typically can provide local authorized repair...Thanks[/quote]

No, I haven't personally. The original tech did. I will ring them and see what they say.

Thank you.

Wayno said:

You should contact Westside DIRECTLY...

Westside Distribution

100, Fifty Pitches Road, Glasgow, G514EB

P: +44 0844 326 2000
F: +44 (0) 141 248 4813
http://quickfind.me/mesa

Click to expand...

Thank you,

Really hoped there was one closer to home though. Courier services in England are notoriously crap to be frank, I should know I used to sub contract for them, and I really don't want to have to trust them with my Mark V. Not to mention that would cost a small fortune too only for them to lose it or damage it further. That leaves me with a good 12 hour round trip to get to Glasgow and back home, twice if I have to leave it with them ( more than likely ).[/quote]

You've spoken with their Service Manager already? He typically can provide local authorized repair...Thanks[/quote]

No, I haven't personally. The original tech did. I will ring them and see what they say.

Thank you.[/quote]

Apparently Westside have offices in London, Wayno. Much closer to you than Scotland. Maybe they could ship it from there internally/properly as opposed to Johnny Courier...? https://www.westside-mi.com/


In other news: Dide the tubeswap in V2 of my friend's V:35 today.
Totally worked. A Ruby this time instead of standard Mesa. (The store only had that one)
But the same transformation occurred, and with the extra glass in the back of the 35 it was devastating in size and low end. And the same gain and pre-EQ enhancement. He and his Les Paul Goldtop absolutely loved it.... And the look on his face seeing him utterly forfilled and feeling it was all the reward needed. Then we jammed (Me on the III, through the EV combo and a 1x12 extension cab, and he was playing the 35 through the v30 2x12 recto cab.
Unbelievable sound both individually and collectively.. Truly titanic.

I have not played through a Mark V:25 or V:35, is the difference all that much?

I returned back to 12AX7s recently and that is just as great as the 12AT7s. Sounds great either way.

I am saddened to hear of no avail on the repair of Wayno V. I still doubt it is associated with the mute circuit (I did send a PM a while back wayno, check your inbox). It has something to do with the large ribbon cable next to V4. Signal have to make it to the back PCB for the FX send jacks and I believe that is also where the relay is to switch out the FX (switch is there too). If the circuit is broken on one of the wires there will be no send, return, turner out, or signal making its way to the phase inverter. I think once the amp gets into the right hands the diagnostics done by Mesa service or there techs abroad should be able to isolate the issue as well as fix the problem.

bandit2013 said:

I have not played through a Mark V:25 or V:35, is the difference all that much?


I am saddened to hear of no avail on the repair of Wayno V. I still doubt it is associated with the mute circuit (I did send a PM a while back wayno, check your inbox). It has something to do with the large ribbon cable next to V4. Signal have to make it to the back PCB for the FX send jacks and I believe that is also where the relay is to switch out the FX (switch is there too). If the circuit is broken on one of the wires there will be no send, return, turner out, or signal making its way to the phase inverter. I think once the amp gets into the right hands the diagnostics done by Mesa service or there techs abroad should be able to isolate the issue as well as fix the problem.

Click to expand...

Well they are a mini AT7 Mark V. Also it wasnt as icepicky to begin with.
And Crunch channel is the heavy, smooth and massive. And after modding, the lead channel is too.
A real beast that kept up with the Mark III well at the vols we played at.

Theres hope not only in Westside, in Essex amp repairs.. as a last more-local resort.
I'd definitely take Mesas' advice. They probably know of E.A.R and may refer you anyway Wayno.

If you're right about the printer cable, Bandit, then maybe the old soldering iron trick would have worked...? The same they used on the ribbon cable of the VDU-dot matrix screen of the Gameboy, when they would fail, due to the frail cable.. To gently and quickly run the soldering iron across it to heat and resolder/connect the cable again with many quick light passes over each wire in the lead until they are reunified. Look up 'Gameboy Dot Matrix Ribbon cable Soldering iron' on YT and you'll see what I mean. Just a thought.

Not sure the iron would work as this is an insulation displacement type of connector, heating up the wire may pose issue if the insulation is drawn into the terminal due to thermal wicking. Also, insulation displacement type of terminals also place a strain on the wire itself when it gets staked onto the connector by pressure. It is more common to get a broken wire if too much movement or flexing of the cable has been done. Generally that type of wire termination is reliable and has many uses including phone hubs and such. That being said, the one problem that is prone to occur may be copper corrosion from humidity and heat. Well lets suppose all of the wires in the ribbon cable are good and connections are intact. Based on basic diagnostics the next culprit would be the solder joint on the pin headers. If all is good, then follow though with circuit analysis to trace the wires to the PCB and associated components.

I did find a schematic on a Nomad that included the switch logic, I believe there are a few others too that have it (including the Road King II). There seems to be a common theme here, Some of which is performed with transistor and diode circuits as a crude logic format and then there is the unexpected LED driver chip more commonly used with bar graph displays or dot matrix display. The LM3914 (yeah it is an LED driver chip that uses an array of comparators that pull in circuits using open collector outputs). All of the relays and associated circuits for switching all feed into one circuit controlled by a 2N6426 Darlington transistor. Since there are no MOSFETS to be found, I doubt that there is reason to believe a transient may have caused issue. Still that is probable. All I can do is speculate what the issue may be so perhaps I need to revert to silence as assumptions may be misleading without identifying the component(s) in question. Was the side effect of operating the amp without the cable connected the root cause of the issue? I had done the exact same thing when I removed C39 and forgot to reconnect the ribbon cable. No sound and a bit of motor boating was the end result (motor boat tap was from a preamp tube causing noise to find its way to the phase inverter probably though ground).