Mesa Subway Static Riddle?

soundchaser59

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I've had this Subway Rocket 44 a few months, and it has been flawless until tonight.

(at home in the basement, amp hasn't been moved in several days)

Suddenly it starts making this static noise, sounds like arcing, like a tube mightbe going out. But these are all new tubes, JJ and EHX. I unplugged everything from all of the jacks and the noise continues.

Turn all the knobs and the noise is still there. In fact, one knob - the rhythm gain knob - makes the static noise louder when turned up, but the noise remains when the knobs are turned off. None of the knobs makes the noise softer or makes it quit, and the rhythm gain knob is the only knob that can make the noise louder. Not even turning the masters up made the noise louder.

So I start tapping, and everywhere I tap I can hear the rhythm of my tapping in the static. The static noise is constant, and if I tap on the knobs, the static also matches my tapping. If I pound my fist on top of the amp the static stops for a minute or so, but it always returns.

The static reacts most of all when I touch my guitar cord to the rim of the input jack.

Some kind of rogue grounding issue? Loose wire? Loose solder joint? Something touching the chassis that shouldn't be touching??
 

soundchaser59

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I have another EL84 amp sitting here, I'll switch tubes tonight and see if the issue goes away.

Darn it......I was hoping "new tubes" meant "good to go for at least a year without any problems." The tubes did come with the amp when I bought it, but they are not "my brand" that I usually buy.
 

teefus

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I have another EL84 amp sitting here, I'll switch tubes tonight and see if the issue goes away.

Darn it......I was hoping "new tubes" meant "good to go for at least a year without any problems." The tubes did come with the amp when I bought it, but they are not "my brand" that I usually buy.
don't forget to swap the pres too. if it is the rhythm gain knob making the most noise it might point to that particular tube in the preamp section.
 

soundchaser59

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BUMMER!

All new tubes, new preamp tubes, new power tubes. Played for 3 hours tonight without a glitch. Then the last two songs I turned both channels up just a hair and the static suddenly returned. Almost constant, I couldn't play anything without the loud arcing noise. Even if I turn the guitar volume way down and play soft, still had the arcing static noise. Which I hope means it isn't the speaker, which is a minty Weber Legacy 100 watt that I bought mildly used.

This sucks big time. I can't afford to have a tech go over this thing, but what else can I do......

I called Mesa today and the tech said I could easily spend $300 bucks by the time I let them go thru it and send it back......and they might not find anything more than bad tubes or dirty sockets. Main problem is getting the amp to have the problem while it's on their bench! If they can't recreate the problem, they probably can't fix anything.

I still think I should try my hand at doing some type of bias mod on this thing, so it will run just a shave cooler. I'm gonna yank the chassis out tonight and see what I see.....

Sucks especially because I need to be able to trust this thing for gigging. I have a back up, modded DC3 that's been gone over well recently, but I don't love the idea of lugging around two Mesa combos to every gig. I should save up for a Mini Rec and use that for a backup. Man I hate the thought of playing a gig and suddenly having mic'd thunder static coming thru my amp in the middle of a set.
 

soundchaser59

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I did get in there tonight and deoxit the tube sockets and clean the jacks, including the footswitch jack. Realized I still had the MEsa preamp tubes in, so I took the new Tung Sol's out of the other amp and put those in the SR44. I was told the JJ's are new, so I have those in there as well, but I have some new EL84's on the way also.

I believe my SR44 has already been modded. In the schematic, for the bias supply section, it shows a 120K resistor after the 15K and 33K. It appears that (if there ever was an actual 120K resistor there) the 120K has been removed and in its place is a 15K and a 100K soldered together in series. It's a very clean job, but I doubt that the factory would have done it this way, so I'm assuming it has been modded. I guess lowering the Rk at this point would very slightly lower the bias voltage? I still think it runs fairly hot, but I'm not inclined to mess with it right now unless the problem continues.

Sorry for the poor photography skills, but you can get the idea of the resistor mod here....... you can see the resistor magic in between the blue caps and the red wire. (I swear there is not a single 33k - orange, orange, orange - resistor on this entire board! I couldn't find one!)

 

soundchaser59

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When I called Mesa I said, "I have an old Subway Rocket 44...blah blah...." and the guy's first comment was, "Those aren't that old. When we say old, we mean from the 70's! That amp isn't really old enough to have capacitor issues." He seemed to think that 15 years should still be well within the strong and usable life of this amp and all of its components.

On a sad note, our premiere amp tech here in Lincoln (Chuck Mathes, Mathes Amplification) died unexpectedly last Thursday. I was actually planning to let him look mine over, and had sent him a message Sunday night. Then Monday morning the groups on FB were buzzing about news of Chuck's death. (The only authorized Mesa dealer and service guy in my state was in Omaha at Russo's, and they just closed their doors.)
 

soundchaser59

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A small step for man kind......

Took out the Mesa preamp tubes, took out the Fender "GT" (Sovtek) EL84's, doused all tube sockets and footswitch jack with deoxit, cleaned all 1/4" jacks.

After all this I put 'er back together (new Tung Sol preamp tubes, and supposedly new JJ EL84's) and played 'er loudly (louder than Sunday night when I had the problem) for 2 hours without a single glitch! Just killer sound, pure and simple. Hope this is all it needed. This amp did come from the Bay Area, so maybe a bit of Pacifica humidity took a small toll over the last few years? :phones
 

Blue Strat

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It's possible that all you needed to do was remove and reinstall the existing tubes. Symptoms as you described them rarely come from the tubes themselves, but the connections between the pins and sockets are another thing entirely.
 




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