Mark IV problems... help needed

[F1-Fanatic]

First let me say that my new (1991 Mrk IV-a Combo) has been acting very strangely lately and I have no idea where to start.

First, I was playing a few days ago at very low volume (Tweed at around 1) when all of a sudden the sound just died to a very low level. I switched the volume off and then it was very loud again. Weird... So I continued playing and all seamed fine for about 20 minutes when it happened again.

Now (2 weeks later) whenever I play a clean tone I hear this (for lack of a better definition) "warble" sound almost like a quick tremolo. I bought the amp used and have no idea if it was ever re-tubed or had any work done, but the amp is in mint condition w/ a hardwood cab and wicker grille.

Any thoughts on where I should start???

 

[Russ]

Being that you don't know the condition of the tubes I would say a good place to start is with a full retube. Then you can swap the old preamp tubes in one at a time to figure out which ones are useable spares. Then you can swap the old power tubes in a pair at a time to see which pair is still good for useable backups also. Mesa says in the owner's manual that most of the problems experienced by the owner can be fixed by replacing the tubes. The tubes would definitely be the first place I would go to start troubleshooting. It sounds like you are having a tube that is getting ready to fail.

 

[Tuna141]

I agree with Russ - the first thing to do is check the tubes - most likely that's all it is. Good luck.

 

[F1-Fanatic]

Okay cool... Which tubes do you guys recommend? I have heard not so many good things about the Mesa branded tubes. Any recommendations?

 

[Russ]

Check out some of the recent posts in the tubes section of the forum. I would personally not put a JJ in V1 but I wouldn't use Mesa's SPAX7 in there either. Try a GT12AX7M or Tung-Sol in V1. Then the rest can be nice supporting tubes like C9's or JJ's if you want to keep it cheap. Sovtek LPS is another nice tube for general purpose though I don't think I would want it in V1. Those are a little more than the C9 and the JJ. Just pay attention to V4 though because you have an older (A) version. This will need to be a nice 12AT7. I have a JAN Phillips 12AT7 in mine. I also have an EH that doesn't sound too bad in there either. If you use a 12AX7 in there be prepared for not such nice results in your reverb. Otherwise, just get nice 12ax7's to fill the rest of the V2,V3,V5 positions. You can use Mesa tubes there but they are basically just screened Sovtek WA's (Sovtek's cheapest tube) if I remember that right. You will probably get better results form the C9 or JJ. If you want screened C9's or JJ's get the GT versions. For that matter, you can also get a GT 12AT7. At least this way, you will not have microphonics or noise issues right away and if you do you can get replacements free for 180 days because of their warranty. This might be your best option if you don't like having to buy new tubes all the time. At least this way, it doesn't cost you to replace a tube that goes bad right away.

 

[F1-Fanatic]

Check out some of the recent posts in the tubes section of the forum. I would personally not put a JJ in V1 but I wouldn't use Mesa's SPAX7 in there either. Try a GT12AX7M or Tung-Sol in V1. Then the rest can be nice supporting tubes like C9's or JJ's if you want to keep it cheap. Sovtek LPS is another nice tube for general purpose though I don't think I would want it in V1. Those are a little more than the C9 and the JJ. Just pay attention to V4 though because you have an older (A) version. This will need to be a nice 12AT7. I have a JAN Phillips 12AT7 in mine. I also have an EH that doesn't sound too bad in there either. If you use a 12AX7 in there be prepared for not such nice results in your reverb. Otherwise, just get nice 12ax7's to fill the rest of the V2,V3,V5 positions. You can use Mesa tubes there but they are basically just screened Sovtek WA's (Sovtek's cheapest tube) if I remember that right. You will probably get better results form the C9 or JJ. If you want screened C9's or JJ's get the GT versions. For that matter, you can also get a GT 12AT7. At least this way, you will not have microphonics or noise issues right away and if you do you can get replacements free for 180 days because of their warranty. This might be your best option if you don't like having to buy new tubes all the time. At least this way, it doesn't cost you to replace a tube that goes bad right away.

Russ,

Thanks for your advice. Problem is I am a noob when it comes to this stuff, so your answer was a little bit ove rmy head but I will check out the "Tubes" section and bring your advice with me when I go to purchase tubes. Thanks for the quick, and detailed response!

-Norman