What the hell, MORE Mark IV problems

[ajtooke]

I'm trading up my Mk IV head for a combo version for easier transportation, especially at school next year. This one is ~2001 B widebody combo, looks like it's in great shape. But when I play past certain volumes (2 on master 3 on rhy2 channel for example - not too loud - full or tweed and 30w setting) through the Clean and RHY2 channels, it breaks up horribly and sort of cuts out with this ridiculous oscillation sound. I'll hear alternations between horrible tone and nasty silence in an oscillation pattern, along with the other channels light lighting up. For example if I'm playing on the green light clean channel, and strike a note, I'll get the sound and the orange rhythm2 light will blink slightly on and off randomly.

Lead channel is normal and sounds *OK* - not spectacular and has a harsh high end to it, maybe due to the open back and vintage 30 speaker. It also only happens with low notes, particularly when struck hard or when channel volume is higher. The low B of my 7string brings it out nicely (by nicely I mean horribly of course).

I'm really upset about this, and am ready to just say screw the whole Mark IV line and Mesa in general, I've had nothing but problems. I know there are people in this forum that probably already know what the problem is, I'm wondering if you can estimate a cost to fix. I've tried to completely different sets of tubes by the way, even using EL34's and 6L6's in the outside power tube sockets.

Thanks,

-Alex

 

[fdesalvo]

I think your relays are taking a dump.

 

[ajtooke]

I think your relays are taking a dump.

Figured it was something like that, but where exactly are they in the circuitry? Could I fix it myself if I'm OK with a soldering iron, and if not how much is it gonna be to get fixed? And why is the lead channel unaffected?

AND WHY DID THIS HAPPEN with what is supposedly one of the most reliable amps out there?

 

[fdesalvo]

Dude, I wouldn't be able to tell you without looking at the schem, but it's something that you don't want to take on if you don't have experience working on tube amps. These amps store enough electrical energy to kill a man.

 

[ajtooke]

Dude, I wouldn't be able to tell you without looking at the schem, but it's something that you don't want to take on if you don't have experience working on tube amps. These amps store enough electrical energy to kill a man.

Point taken, thank you. You don't how much it would cost though, or why it would happen in the first place? I'm pissed that I managed to get two Mark IV's that have needed repairs, probably the worst luck in history.

 

[fdesalvo]

Dude, I've no doubt that you are sharp enough to change the relays, and I'm glad you decided to leave it alone! I could be wrong, but that's what my friends MKIV did and the tech changed the relays and all was fine after.

I'm not sure how much it will cost, but Mesa's bench rates are actually reasonable if you can't find an authorized tech nearby. I'm sure someone will chime in with another option, though.

Oh, and I hear ya about the luck...

 

[phyrexia]

Why does it have a Vintage 30? That would make me think that somebody blew the speaker before, replaced it with something they had handy. Or maybe there was something wrong with the amp that blew the speaker.

 

[fdesalvo]

^Maybe the person liked the v30. It's not my cup-o-tea, but I hear ya. It's way underpowered for this use, IMHO.

 

[phyrexia]

well yeah but seems silly to put a 60w speaker in an 85w tube amp.

 

[disassembled]

Try unhooking the footswitch, switch channels manually and see if the problem persists. Try hooking into a different cab as the speaker might be rattling some component to death on the circuit board. It is impossible to estimate a repair cost when we don't even know what is physically wrong. The repair person might be a thief or a very honest person so that plays a part in the price as well.

To me it might be the logic circuit for channel switching but that is just a speculation.


If the tubes are the original Russian 2's and STR 430's then I bet it is way overdue for a retube. The widebody combo was never known for producing a thumping low end. You will need some sort of closed back cab if you are looking to have a lot of thump. This purchase probably was a step backwards as far as having the tone you're looking for in a single package. The short head with a Thiele is probably the best compact solution IMO. I also own the Widebody combo and think it sounds great but sounds much better through a 412 cab.

I suggest getting a C90 or 100watt + to put in the combo for now. I've read good thinks about celestion's 100 watt speaker so you might want to give that a look.


As a side note about the reliability of products:

You have a used amp that could have been severely mistreated for years and now that is shows signs of problems the previous owner was quick to get rid of it. No amp company, or any company really; for that matter, will ever have a perfect track record. I have had my share of problems with Mesa amps but they were all related to component failure or previous owner abuse/neglect. When it's all said and done Mesa is a stout company that does make reliable equipment, but it's too bad components fail, AC lines surge, ignorant people abuse their products, etc. You get my point.... If you think Mesa is bad imagine spending 3 or 4 times what a Mesa costs only to get something that is less reliable and requires constant maintenance. Mesa is not the best amp company nor is it the worst they are a just one among many so if you are ditching the amp i don't think you will hurt anyone's feelings here. Ii just hope you get the amp fixed so we don't have read someone else post about your amp having the same issues.


Greg

 

[ajtooke]

I've used both the footswitch and the channel switch in the back. Used both the combo speaker and a 1x12 extension, and multiple guitars. I switched tubes to a couple new Mesa 440's and JJ 6L6's and also 5x JJ 12AX7 which worked fine in a different amp and it's the same thing. I plan on putting a Mesa C90 in the combo and I'm sure I'll be happy with it once I get it working - I was gonna just sell both Mark IV's and be done with it, but I played live with a different one last night and it sounded beautiful - so I'm gonna keep it. I figure once all is in working order it will be reliable as hell for many good years.

Anyway, new discovery - the oscillation really only happens at low volumes when I hit a C note. Only certain C notes trigger it - 8th fret E string and 10th fret D string. 1st fret low B string (7string) doesnt do it no matter how hard I hit - this is with clean channel at 6 and master at 1. If I turn the master up to 3 I can make it happen over a wider range - one half step above and below the C, this time including the low B string, and also E and F on the low E string. The rest of the notes sound distorted but don't make the orange R2 light turn on. Does that make it clearer what the problem could be to anyone? I have to wait until Monday to call Mesa and really just want to find out what's going on

Thanks