New Amp(Mark IV), First Post/new member, and I need help!!!

[TenaciousJP]

Hi there,

My name is Jordan, other wise known as TenaciousJP on the forum name. This is my first post ever made too.

Anyways, three days ago I got a Mark IV compact combo. And I've noticed a problem with it.

It has to do with the Triode and Pentode switch. When ever I turn to Pentode all the channels go out of whack making all these buzzing, flopping noises. But when in Triode...it's fine a little back round buzz on the lead channel, but that's normal with every tube amp.

Anyways, I have no idea what's wrong with it. The noise only reoccurs when I have the Power section on Pentode and Simul Class. On other combinations there is no noise like this.

I spent all my money on this, and have no money at all at the moment. If someone can assist me with this I would extremely appreciate it very much!!!

Thanks
Jordan/TenaciousJP

P.S could it possibly be the power tubes? or???

Thanks again!

 

[Shep]

sounds like a tube, power tube. If the Amp is second hand then it most likely could do with some new power amp tubes. they really should be replaced once a year.

 

[WillPlayForFood]

+1 on the almost guaranteed probability of it being a power tube issue. The Triode/Pentode switch effects the power tubes and how they are or aren't running. Pentode runs all your power tubes, so if that's when you are having problems, you can almost positively say it's a power tube problem. For me, while you could change out only a pair, I would get a new quartet of tubes and be done with it. I personally like to change them all at once,too hard to keep track of the pair I have switched otherwise. You might even pick up a couple spares with you're at it :mrgreen:

 

[TenaciousJP]

+1 on the almost guaranteed probability of it being a power tube issue. The Triode/Pentode switch effects the power tubes and how they are or aren't running. Pentode runs all your power tubes, so if that's when you are having problems, you can almost positively say it's a power tube problem. For me, while you could change out only a pair, I would get a new quartet of tubes and be done with it. I personally like to change them all at once,too hard to keep track of the pair I have switched otherwise. You might even pick up a couple spares with you're at it :mrgreen:

Hmm but it only when I run it in Simul Class and Pentode, not Class A Pentode/Class A Triode/Simul Class Triode.

I'm not sure. How bout if I swap the inner tubes(6l6s) with the outer tubes(6l6s) and run it class A pentode and triode?

 

[WillPlayForFood]

OK Teneacious...I misspoke earlier. The Simul/Class A switch is the tube selection. The Triode/Pentode is the a power regulation switch, where Pentode has more power and a harder clip and Triode gives a bit more of that spongy/sweet feel. So, you could run it in Class A and conceivably be fine with either Triode or Pentode. What you are sacrificing is a part of the versatility of the amp. It won't hurt anything!! I ran it Class A Triode for years when that was my main rig. However, I used a midi foot controller to switch all the options on the amp, to get the different sounds. This is one reason the Mark IV is so awesome, it is NOT a one trick pony :mrgreen:

Have fun!!!

 

[TenaciousJP]

Hey guys!

So I removed all the tubes out just now....and guess what I found???

The Mark IV I got had all 6L6's...and one of them the little plastic part of the power tube in the center of all the progs was broken off. And a little glass tip was showing...

Could this possibly be the culprit?

I'm afraid to put it back in now...I might as well wait 2 and a half weeks until I get money and purchase 4 new power tubes.

But...it still doesn't really explain why I was able to use simul class with triode, and class A with pentode and triode. weird.

I don't think it would be okay to put that tube back in the socket....I wouldn't want to damage the amp. would it?

Sorry I've been asking so many questions...this is my second tube amp(first being a long head blue stripe, which i only owned for 4-5 months).

And one last thing, If I were to put EL-34's in the outer power tube sockets...do I have to re-bias the amp? or can I just swap them in?

Any insight with be greatly appreciated!
Thanks
Jordan/TenaciousJP

 

[WillPlayForFood]

Just realized yo have 2 posts going on the same subject. Anyway, the Pentode/Triode switch regulates power or voltage to the tubes. It may be that your cracked/broken tube is fine when running at the Triode level, however becomes an issue when the voltage is stepped up. Weird yes, yet not beyond the tube insanity that is possible :shock:

Only way to tell for sure is to switch out the tubes or take it in and have a tech run some diagnostics on your tube sockets, check the switch, etc. Maybe there is an issue that caused the tube to rupture. Probably it broke in transit and you switch it and you'll be fine.

Let me know if you experiment with the EL34's, I hear that is a cool tone. I have never done that myself.

Happy Hunting :wink:

 

[TenaciousJP]

Just realized yo have 2 posts going on the same subject. Anyway, the Pentode/Triode switch regulates power or voltage to the tubes. It may be that your cracked/broken tube is fine when running at the Triode level, however becomes an issue when the voltage is stepped up. Weird yes, yet not beyond the tube insanity that is possible :shock:

Only way to tell for sure is to switch out the tubes or take it in and have a tech run some diagnostics on your tube sockets, check the switch, etc. Maybe there is an issue that caused the tube to rupture. Probably it broke in transit and you switch it and you'll be fine.

Let me know if you experiment with the EL34's, I hear that is a cool tone. I have never done that myself.

Happy Hunting :wink:

The one power tube is just missing the middle plastic socket piece, that's all. The rest have it. But I checked the sockets and the plastic part wasn't even there. So this must mean it wasn't there in the first place. I have to call Mesa tomorrow and see what they say. This is frustrating.

Just one other note, I've only ran the IV in tweed mode not full power....simul-class works on tweed mode alng with triode and pentode...right?

 

[kmanick]

yes it does.

 

[TenaciousJP]

Okay so I called Mesa today, and told them the problem.

They said the earlier model Mark IV B versions (1993-1994 and some 1995's) had this problem. And the rep said that I need a resistor or two replaced. They said it's a easy fix.

I asked if it had anything to do with the tube(s), he said no it is internally in the amp.

So it looks like it's going to cost me a 100 or so for the check up and fix...which isn't to bad. As long as it's 110 working after.

Thanks for all the help guys!!!

Much appreciated!

Jordan/TenaciousJP