Musician Gear & Tech Discussion

I bought a 100 watt tube Carvin combo amp recently.

I was playing on it the other night and it shorted out. It has a push button reset and fired back up. I noticed that when I wiggled the input with the guitar cable that it shorted out again.

Ive never really been an amp repair guy, I didnt spend a lot of money on this amp, so Im curious what some of you amp guys would do.

I know first to take the amp out of the cab. But Ive always been told that the capicitors in tube amps store voltage and can shock you if you dont know what you are doing.

Just looking for some advice, I dont think it will be a huge issue, but what are some of the dos and donts if I take it apart?

Thanks in advance

Beware of the power caps!

Easy enough to stay away from them if it is just an input jack.
I used to slide the chassis out of my old Fender Bandmaster all the time to do stuff on it and never killed myself, and I didn't know squat about capacitors!

Eric ( our bassist ) has fixed some amps and speaker issues simply by blowing out the jack with canned "air" and cleaning them with rubbing alcohol.

Your issue sounds more like a loose wire at the jack that needs a dash of solder.
The charge at the capacitors can be safely discharged, but it's not something I have much experience with . . . so I just stay away from them.

My daughter wanted a guitar last year. I scanned Craigslist and found a nice lefty MIM Strat. I also spotted a used Peavey Rage selling for a reasonable price that looked perfect for a beginner. When I got to the seller house and tried the amp there was a terrible noise. I wiggled the jack and it started making even more noise. I assumed it had a loose solder joint on the PCB. A lot of modern amps have the input jacks mounted directly to the board. Flying leads (when the jack is mounted to the chassis and wires are run from it to the board) are more common in older amps. Not wanting to have to make a repair on maybe have more to deal with I said I would pass on the amp. The seller kept dropping the price as I walked away. I told her the repair is pretty simple and she will probably be able to sell it but she should add that it has a shorted jack to her listing. In a last ditch effort to move the amp she asked "will you take it for $15. I just want it gone." At that price I figued it was worth a gamble. When I got it home I pulled it from the cab and reflowed the solder joints for the jack. It took maybe 5 minutes and most of that was just waiting for the iron to heat up. I fired it up and it was as good as new. It's pretty much that simple.

Regarding the filter caps in tube amps, you are correct. They store a high voltage charge like a battery even after the amp is unplugged. I find the easiest way to discharge them is to play my guitar through the amp and pull the plug from the wall while still strumming the guitar (with the amp on) until the sound fades completely. Then I unplug the amp and pull the chassis and connect a wire with an alligator clip on one end to the chassis and VERY CAREFULLY touch the other end of the wire to each terminal of the big electrolytic caps in the amp (the one's that look like big metal cans). I do this with one hand at my side. Putting one hand on the chassis and touching something with a charge would cause the voltage to discharge across your heart. Talk about riding the lightning. Instant defibulator.....not good at all and something to avoid at all costs. That discharges any remaining voltage. I even made a tool for doing this by mounting a 10W wire wound resistor inline in my discharge wire and covered the whole shebang with shrink tubing. I put alligator clips on both ends. The resistor helps knock down the spark if there is a little more than normal voltage in the cap I'm discharging. Typically the caps only have a few volts after using the pull the plug method so I've never really encountered sparks. Some dudes just do it with a long screw driver and let the sparks fly. I wouldn't dream of doing that. Then check the caps for voltage with a DMM before touching anything. If you are unsure of your ability to do this take it to a pro. Fear is good...it keeps you on this side of the grass. The problem you are describing is a minor, inexpensive repair and is a pretty common issue with board mounted input jacks.

HDriffraff's advice is spot on. More than likely you are not going to be anywhere near a filter cap while working on the input jack/preamp section but you should ALWAYS both short the caps and verify they are shorted with a dmm.

For a laugh... you can find all kinds of youtube vids of pros showing you how it's done and shocking themselves in the process. Just goes to show you how easy it is to do something stupid even if you know what you are doing!

Good luck and above all be careful.

thanks guys its just a spare amp, so I may take a shot at fixing it myself

Sounds like a loose wire or cold solder intermittent connection. This might be a really easy fix, might not. I would pull the amp head out carefully by not making contact with capacitors, reconnect it all and fire it up to test it. After carefully insulating yourself, start from the input jack and poke around a bit to see if you can find the culprit. If you wiggle a wire and the signal goes in and out... Bingo! You found it. Re-connect or re-solder and you are back in business.

A common problem is that the input jack will loosen up over time and a musician will tighten the nut without holding the back of the jack still. It twists and binds the delicate input wiring causing a short or broken wire. Lots of other possible problems but this is a great place to start looking.

Good luck!

So last night I turned on the Carvin and dont have any volume at all out of it, its 100 watts tube and I cranked it and no volume, I wiggled the input to see if it would short out again, but nothing, maybe I will take it to someone that knows something more than me!

Oh Well, I knew it was too good of a deal to begin with!

So last night I turned on the Carvin and dont have any volume at all out of it, its 100 watts tube and I cranked it and no volume, I wiggled the input to see if it would short out again, but nothing, maybe I will take it to someone that knows something more than me!

Oh Well, I knew it was too good of a deal to begin with!

John, I am curious is it an XB 100?

Haley honestly Im not sure its older the white faced combo, I will have to look at it again and post back. I know its 15 to 20 years old.

Our singer had it, I bought it, a Les Paul and then a 12 string from him over the past several weeks, hes been kinda in a bind money wise.

I hate to post this but the amp is giving me issues, the LP i played at our last gig and the volume on it went up and down, I thought it was my wireless, well found out the other day its the guitar, I cleaned up all the electronics and stuff but its still doing it so I took it to a tech.

The damn 12 string, its a Martin, not one of the high end ones, but the top is laminate and it had warped, so Ive got it at a teck also. He says it will take alittle time to clamp the top and get it back straight.

If my singer has something else he wants to sell I think I will pass! LOL!

Singers don't know how to treat equipment (except mics - sometimes!)

LP problem - sounds like either the pickups need to be rewound or there is a bad connection somewhere.
Martin - if the laminate top warped, that sucker must have got really waterlogged. Did the edges stay together at the binding? The bridge will probably pop next.

Check the fuse on the amp?

Mike I didnt look the Martin over that well when I got it, like I said I was just trying to help out and he needed money and adding a 12 string was cool, Ive never had one.

Yea the bridge had popped up a little in the corner, it doesnt look like it got wet, but if I know Kevin, he probably left it somewhere in the heat like in a truck or out in some closet, we have extreme humidity here, and I imagine thats what messed it up. The tech guy said its not that big of a problem, he said a solid top would pull back faster than a laminate. So I have my fingers crossed on that one.

The LP isnt a problem either to the tech.

The amp doesnt have a fuse it has a little reset button on it, I will get around to it, but its not that high of a priority. I had it hooked to one of my 4x12 before it started having issues and it sounded great, so we shall see..


Just a few more things to put on my list.........................

Right now far more important are the washing machine and dishwasher, seems like when one thing decides to go around my house all hell breaks loose! LOL!

Plus I need to be prepping for my Aint Yo Mama gig sat night, yesterday after work I decided to cut the grass and the damn belt broke on the mower, finally got one on it, but it killed a lot more time than I had planned, oh well, like i said when it rains it pours, I could add about 20 more things to this list, so if you are having issues with anything dont feel lonely cause Im with you!

My wife started complaining about our dishwasher the other night! I said "you're looking at your dishwasher!" The one that came with this house is old and has leaked since I bought the place, so never used it. There's only 2 of us, it takes 5 minutes a day to wash dishes (10 if my wife has used 8 sets of everything to make some fancy dish), why would I want to spend $300 for a new dishwasher, plus $100+ to get it installed and then watch my water bills go up, too?

My wife started complaining about our dishwasher the other night! I said "you're looking at your dishwasher!" The one that came with this house is old and has leaked since I bought the place, so never used it. There's only 2 of us, it takes 5 minutes a day to wash dishes (10 if my wife has used 8 sets of everything to make some fancy dish), why would I want to spend $300 for a new dishwasher, plus $100+ to get it installed and then watch my water bills go up, too?

Dishwashers are EASY to install it takes an hour at most. You'll actually use less water with one. Rinse off dishes load them in the dishwasher when its full you start it. Easy peasy! I admit this does work better with more than 2 people. If your like my wife and I. We purchased a new house (10 years ago) bought all new appliances. Unfortunately new appliances these days only last 10 years as a result they all start breaking at the same time. I'm with you when it rains it pours!

LOL the dishwasher works it just doesnt rinse the dishes properly, I took the filter out and cleaned it and it still doesnt work.

Yesterday I fixed our washing machine, basically the whole tub, pump and motor assembly floats on four rods with springs on them. I got all four in and its back working, so no laundermat time, that was a close call.

I agree with you haley things just dont last at all anymore, that dang waching machine, while I had it apart there is really nothing to it. Its a nice washer but its built so cheap its scary when you open in up.

Haley I forgot to look at the Carvin and get the model off of it.

I think its something like MDX 100 or something like that, I just had other things to do yesterday and last night and never got around to looking at the amp.

Ive got a gig this weekend, so I just plan on using my cut to put the amp in the shop and get straightened out.