MARK IV PROBLEM

[Nick_cor]

I just bought a MKIV off a guy 2 hours away. It was playing perfectly until a couple hours ago, I noticed that I get volume changes. Does anyone know what's going on! I'm scared! :shock:

 

[rockhound76s]

If I'm understanding you correctly, you say that when you play you are experiencing volume changes?

Volume swells and drops are characteristics of worn out power tubes, perhaps new tubes would help. Do you know if the tubes have ever been changed (especially since it is a used amp)?

 

[Nick_cor]

If I'm understanding you correctly, you say that when you play you are experiencing volume changes?

Volume swells and drops are characteristics of worn out power tubes, perhaps new tubes would help. Do you know if the tubes have ever been changed (especially since it is a used amp)?

Hey thank you for responding so quickly, I know that the original owner of the MKIV had it in a studio and sold it to someone who left it in his room, and the person who bought it off him which is the person I bought it off of, said that he barely turned it up. I am the fourth owner! The guy I bought if off of had it for a year and 4 months. He said the owner before him had changed the tubes "recently". I'm somewhat concerned because the amp was cranked 2 times from its previous owner, and the tubes were changed from the guy before him.

I pray to god it's a tube problem because I love this amp, it's the sweetest thing ever!

 

[JOEY B.]

I bought a MK IV off Ebay about 6 weeks ago that had a similar problem with supposedly recent new tubes. The preamp and power tubes were removed and packed seperately for shipment. The problem was decreased gain or level after about 15 minutes of loud playing. I replaced the power tubes with some spare 6L6's with no change. Then I tried spare preamp tubes with the same results. TOTALLY pissed off, I grabbed the guitar cord at the input jack, and BOOM the gain was back. I stuck a small flat blade screwdriver into the input jack (with the power off) and bent the contact up, then sprayed contact cleaner on the cord end and intalled and removed the cord several times. No problems since. Volume swells= power tubes. Gain variations might be preamp tubes, input jack or something internal. I did get a complete retube kit from Bob at Eurotubes (JJ 6L6/ EL34) for $104.00 to the door and it sounds great. Good luck with that awesome amp.

 

[JAMz]

While the amp is on and with the stand by switch in the "on" position, try tapping the power amp tubes with your finger nails. Do it gently and avoid touching the tubes with your fingers tips since you'll get a nice burn. Pay attention to what you hear. Sometimes you will find the tube that is giving you problems using this method. I just found a little guy that was giving me a lot of microphonics and feed back in the pre-amp section of my mark IIb using the tapping method. Again be gentle, think of it as your girl friend and you'll get the picture.

Another thing is to check the contacts on your Input, FX Loop Send/Return, Speaker and Remote Jacks. These may get oxidezed, specially is the amp has been stored for a while. Check your reverb conact as well. Spray a little deoxit on a 1/4 plug and insert it and pull it out rapidly a few times in each jack. Clean the plug and repeat. The plug should come clean after sevreal times. Avoid spraying the contact cleaner directly into the jack since this might be harmful to the amp. Do this while the amp is turn off. Also move back and forth all the rocking switches, these can get oxidized as well and sometimes not make a good contact.

I hope this help, God willing you have only a bad tube of faulty contact.

JAMz.

 

[Nick_cor]

While the amp is on and with the stand by switch in the "on" position, try tapping the power amp tubes with your finger nails.

Hey thanks! so by doing this, i should hear something come out of my amp, even if my guitar is not plugged in? what am I listening for? I don't know what sounds are good or bad?

 

[JAMz]

Sometimes when tapping a tube you can hear static, feedback, high pitch squeal, scratchy and popping noises. Usually bad tube will start doing those weird noises once the tube is tapped. A good tube will just amplify the tap and nothing else. Try it and you'll see what I'm talking about.