Mesa MarkV / Saturation 'mod'

[Wayno]

Hey guys, just swapped a jan philips 12at7 in the V4 position and when i turned the amp on, there was no signal. Swapped the original preamp tube back and still no signal. Don't know how I managed to break the amp doing a simple preamp swap, but the thing is f%&# now. Any suggestions what could be wrong?

Hope it is something simple like dlpasco said, fingers crossed your amp is OK. I too have made all the silly mistakes he mentioned before, more than once. These Boogies are pretty tough though and will stand up to some abuse. Lost count of the amount of times I've fired mine up without the speaker connected, trials of swapping between cab and combo speaker.

 

[bandit2013]

Glad you were up and running again. Power tubes usually do not work well in a Diode circuit and vice versa. The amp may even power up and turn the lights on and such since the silicon diodes run in parallel of the rectifier tube (unless you were using 10W mode or CH1, CH2 set at 45W mode with tube rectifier selected. Now I need to find out what really happens when you install a 6L6GC into the 5U4G position.... I looked at the pinout on both 5U4G and the 6L6GC. I do not think there is any risk if you did this by accident since the only way you would get current flow is if the heaters were connected. Heater circuit for the 5U4G also forms the cathode of the rectifier and pins 4 and 6 are the anodes. Heater in the 6L6GC runs from pin 2 to 7 so there is no electrical connection to for the heater. No heater, not electron emission, no current flow and dead amp (only temporary until you get the tubes in the right position).

 

[dcphillip]

Glad you were up and running again. Power tubes usually do not work well in a Diode circuit and vice versa. The amp may even power up and turn the lights on and such since the silicon diodes run in parallel of the rectifier tube (unless you were using 10W mode or CH1, CH2 set at 45W mode with tube rectifier selected. Now I need to find out what really happens when you install a 6L6GC into the 5U4G position.... I looked at the pinout on both 5U4G and the 6L6GC. I do not think there is any risk if you did this by accident since the only way you would get current flow is if the heaters were connected. Heater circuit for the 5U4G also forms the cathode of the rectifier and pins 4 and 6 are the anodes. Heater in the 6L6GC runs from pin 2 to 7 so there is no electrical connection to for the heater. No heater, not electron emission, no current flow and dead amp (only temporary until you get the tubes in the right position).

Thanks, I'm super relieved its not gonna cost me a trip to the repair shop. It powered up fine with all the lights on, but just no signal. Mute wasn't on either. Do you think one of the tubes wasn't sitting all the way firmly in the socket, and that could've killed the signal? I know that's usually not an issue for power amp tubes. Sucks because I went through practice today playing my buddy's Triple Rec as a backup, and then when the Mark V was running again, my ears were totally blown out. I'm still really impressed with how extreme mode sounds.

 

[bandit2013]

Hard to say actually...... I don't think I am going to try it to find out.... Still if you had the tubes in properly, if one was not seated or even removed, the amp will still operate, will not sound as good but it will still function. Not sure what to say there. I would check the fuse for any metal balls on the wire. If you see any or if the wound wire on the fuse does not look smooth it may have been on the verge of going. The Mark V does not have any load protection.

When you had the issue, was the speaker plugged in the correct jack? I have done that a few times. Next time this occurs, take a look at the power tubes before hitting the standby. It may have been a temporary short in one of the tubes. Not caused by preamp tubes. Even if you shorted one out that would not shut down the amp as that would only be a few milliamps, unless it shorted to the heater.

If you had a loose preamp tube that will definitely kill the sound.

 

[dlpasco]

So weird. On a whim, I pulled all the tubes and plugged them back in and now it works fine. Glad that it's a crisis averted. Interesting sound with the 12AT7. Haven't had too much time to play with it, but you can definitely crank the gain more on it. It also seems to take OD's in channel 3 better. Extreme setting is super useful now.

Yeah, Extreme mode got a lot more interesting for me right away. Loving IIC+/pentode, too.

I turn bright on for Extreme and off for IIC+. Haven't really. Done much with Mark IV yet.

I'm glad the problem got resolved. I hate getting scares like that.

 

[Wayno]

Glad you got it sorted. Your post hadn't showed up before I replied ;-) hope you enjoy the change as much as I do.

 

[IronSean]

On the topic of making Dumb mistakes and the Mark V being resilient...

I may have... forgotten to replace the power tube I pulled when swapping preamp tubes to test the 12AT7s and fired the amp up any and played for a few minutes at a time... repeatedly...

 

[dcphillip]

I think the main takeaway for me here is to make sure the preamp tubes are sitting firmly in the socket next time I swap them, haha. Really looking forward to playing around with IIC+ mode after the change. I feel like I neglected it in favor of Mark IV mode prior to the swap. BTW, has anyone noticed a change in the way the reverb level works in Channel 2? I had the reverb at about 9 o' clock before, and now it just sounds cavernous. To the point of turning it off altogether. Works fine in the other two channels, though. I know V4 effects the reverb driver, but it doesn't seem like anyone else has come across this yet.

 

[Wayno]

I haven't really gotten around to playing with the reverb much to be honest. Had it on in CH3 for a bit during the mid section of Orion from master of puppets the other day but didn't notice any distinct change from before. Defo food for thought though. Would make sense if the at7 does alter things somewhat.

 

[bandit2013]

I have not noticed much of a change. Ever since one of the JFETS crapped out the reverb circuit and it just went silent. After replacing the J175 FET (M2) both CH3 and CH2 reverb was loud to start with, much louder than I thought it was. I did not notices much of a difference between a short plate 12AX7, long plate 12AX7, 5751 or the 12AT7. If anyone else notices a change in the reverb chime in and reflect if louder, softer or the just can't tell.

 

[bandit2013]

On the topic of making Dumb mistakes and the Mark V being resilient...

I may have... forgotten to replace the power tube I pulled when swapping preamp tubes to test the 12AT7s and fired the amp up any and played for a few minutes at a time... repeatedly...

Believe it or not, that is a trick to figure out what is blowing a fuse, or if the amp will not power up for what ever reason. The amp will run with a tube missing even one of the center tubes. Outer tube may not be noticeable as much but the imbalance may cause one tube to suffer and possibly red plate if left as is for too long of use. If one of the push pull class A tubes is missing, the amp will sound harsh and terrible on all channels.

 

[Bankim]

There is a JAN philips 12AT7wc Black Plate O Getter tube on some sites and I was wondering whats the difference between the grey plate and Black plate.

Note : I am a noob when it comes to tubes but I did order a Jan Philips 12AT7 (because of this thread ) , which I assume is a grey plate version as the price is lower compared to the black plate.

 

[bandit2013]

One has a black plate and the other has a gray plate. Just a difference in plate coatings. Not really sure if there is a difference.
the tubes I have seen with black plates range from 1950 RCA to 1970 Sylvania. If it is a JAN tube it had to meet specific criteria. \

for your viewing pleasure..... Yeah I did a search on the difference between gray and black plate 12AT7.... The audio tubes site has more information than the others. Does not really reveal much of a difference. Actually where you will be placing the 12AT7 will be quite saturated so the big air and clarity will not apply all that much.

http://www.audiotubes.com/12at7.htm
http://tctubes.com/12AT7-ECC81-5965-6201-tubes.aspx

 

[Bankim]

One has a black plate and the other has a gray plate. Just a difference in plate coatings. Not really sure if there is a difference.
the tubes I have seen with black plates range from 1950 RCA to 1970 Sylvania. If it is a JAN tube it had to meet specific criteria. \

for your viewing pleasure..... Yeah I did a search on the difference between gray and black plate 12AT7.... The audio tubes site has more information than the others. Does not really reveal much of a difference. Actually where you will be placing the 12AT7 will be quite saturated so the big air and clarity will not apply all that much.

http://www.audiotubes.com/12at7.htm
http://tctubes.com/12AT7-ECC81-5965-6201-tubes.aspx

Thank You kind Sir. As always, up to the task !

 

[bandit2013]

I think the main takeaway for me here is to make sure the preamp tubes are sitting firmly in the socket next time I swap them, haha. Really looking forward to playing around with IIC+ mode after the change. I feel like I neglected it in favor of Mark IV mode prior to the swap. BTW, has anyone noticed a change in the way the reverb level works in Channel 2? I had the reverb at about 9 o' clock before, and now it just sounds cavernous. To the point of turning it off altogether. Works fine in the other two channels, though. I know V4 effects the reverb driver, but it doesn't seem like anyone else has come across this yet.

If a preamp tube is not in its socket it is more than likely the cause of no signal or an extremely weak signal at the output. Another means of diagnosis pulling preamp tubes to find out which one is making popcorn noises with not input signal. Generally you start at the front of the gain chain and work your way to the end. I have often done the same thing to determine what tubes are in a channel path and what are not. With the Mark V, all tubes are common to all channels except V2 which is only used by CH2.

With the case of a NOS tube, depending on age, the tarnish may act like a insulation barrier if the socket does not dig into the pin or if the pins are smaller than expected. Not exactly sure what material the pins are made of, most likely copper with nickel or silver plating. My guess it may be silver plating however nickel will also darken when plated onto copper since there is an intermetallic bond that may change contact resistance of the pin. If the pin looks black and is dull that may be a form of tin pest which may be non conductive. I have tried polish some pins with an small nail file. My wife must have bought a truck load of them as they are everywhere. They also work great for honing and polishing fret wire (use tape on the fretboard first to protect the wood).

 

[bandit2013]

One has a black plate and the other has a gray plate. Just a difference in plate coatings. Not really sure if there is a difference.
the tubes I have seen with black plates range from 1950 RCA to 1970 Sylvania. If it is a JAN tube it had to meet specific criteria. \

for your viewing pleasure..... Yeah I did a search on the difference between gray and black plate 12AT7.... The audio tubes site has more information than the others. Does not really reveal much of a difference. Actually where you will be placing the 12AT7 will be quite saturated so the big air and clarity will not apply all that much.

http://www.audiotubes.com/12at7.htm
http://tctubes.com/12AT7-ECC81-5965-6201-tubes.aspx

Thank You kind Sir. As always, up to the task !

I am as much as a novice when it comes to tubes and never really started tube rolling and looking into different variants of preamp tubes and power tubes until late in 2013. Odd that I have owned a Mark III since 1989 up until October of 2012, Mark IV from 2000 up to 2015. Never really bothered to use different tubes in my amps other than Mesa's. (well there was the tube issues back in 1992 when you could not find Mesa tubes at all and had to use GT or other for the power tubes). Never changed a tube in the Mark IV until after I got the Mark V. MKIV had original tubes in it for 13 years (I did not play much for that time period), too bad you can't find those coke bottle Mesa 6L6 tubes anymore as those sounded really good, I even think they were better than =c= 6L6.

 

[bandit2013]

I will definitely compare the cocktail preamp selection I posted earlier with the stock with V4 mod on the Mark V again. I finally got the Celestion Redback to install into the Mark V combo. The MC90 took a break and I installed the EV. Not sure I am set on the EV so have to see how the Redback sounds. If it is anything like the Crème ALNICO 90W speaker I will be extremely happy and may opt to go with the cocktail of tubes vs the V4 mod. Will see soon enough once I get the speaker installed.

 

[Dreamtheaterrules]

Dan, I knew a guy who did something similar one time. What was his name again....

 

[Dreamtheaterrules]

p.s. So, no, not trying to hijack the thread to a tube rolling thread, but... that's one overwhelming "yes" to the Doug's kit, and one "no." Which is why this is all so much fun. LOL One guy loves it, one hates it.... that's what is a bit daunting about the V, honestly. If that tube kit or this mod to V4 makes it into my dream amp, like I thought it would be, I'll kick my own behind for thinking about selling it. IF I sold it without trying both, I'd always wonder. But tube rolling trying to find out the magic combination is an awful lot of trouble when there are this many tubes in the thing. I've come very close a couple times to dropping all new stock Mesa tubes in and and then saying "If it doesn't sound GREAT now, it's getting sold." But I'd hate to think something this simple COULD be what makes it the amp I dreamed it would be.

I've got a 5751. I'll try that first.

 

[jnoel64]

I've read and have been following this thread for a while. Now I am GASsing for a Mark! Trying to decide between a 35 and the full 90 is distressing, though. I don't need the full 90 watts - or, more importantly, the weight of the MKV - and the Cab Clone feature of the 35 is extremely tempting. But the 3 channels of the MKV offer a wider tonal palette. I can't afford either at the moment, but am working on a plan to get one of the two. I may have to sell my RK1 to do so. I've listened to the sound samples of the MKV with the AT7 mod, and I just keep drooling... I suppose I should say "thanks," but I have that "kid in a candy store" mentality going on now....