mikeymike
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can anyone tell me what that is that is burnt? It looks like a resistor to me.. Which tubes does it affect (channelwise). thanks for your time guys
ok forget the story what's wrong with my amp. (pics inside)
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can anyone tell me what that is that is burnt? It looks like a resistor to me.. Which tubes does it affect (channelwise). thanks for your time guys
It's probley a grid resistor. According the the schematic for the 2:100 there are four 1k 2 watt resistors per channel. Or one resistor for each tube. What probley happend is the tube shorted out or the socket shorted out, and the resistor burnt up. You should take it to get it fixed. I don't know how much it's going to cost you though. Depends on the techs where you live. I would susptect it shouldn't cost more than 150 dollars, so even then you still got a great deal.
leadfootdriver
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msi said:
Yep, screen grid resistors. They're like a few bucks. It might be hard to find the exact brand replacement, but you could find an equivilent no problem at your local electronics store. Do it yourself for nothing. Search for soldering, and desoldering tips if you don't know how. This is a real cheap fix.
leadfootdriver
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Make sure you buy new tubes though so it doesn't happen again. :lol: :wink:
mikeymike
Well-known member
msi said:
Hey do you mind telling me where I can get that schematic? I have a multimeter and I can test the amp in diff places.
mikeymike
Well-known member
leadfootdriver said:
Yeah I am able to do that sort of thing myself. I'd really like to replace it with the right brand though. Can you tell me more about blowing these? What causes them to blow? Also what do they do? What do they resist, will it harm the tube? The tube that it's lined up with has a broken key. Do you think the previous owner could have inserted it wrong and blown the resistor?
I really appreciate your responses guys. This forum is awesome. By the way the guy is claiming nothing is wrong with it and that any damages were done by shipping.
leadfootdriver
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mikeymike said:
What he said. A tube might have shorted out, or he played the amp without a load. YOu MUST have your speakers pluged in to the amp before you take it off the standby; for BOTH channels. That's the way of all tube amps.
That very well could be the case. I'd just start with a new set of power tubes.
Well, you can't fry an amp if it isn't plugged in. That wouldn't happen in shipping. :roll: That guy is a jackass. Only a total idiot would break the keys off a power tube from pure carelessness. He jammed the tubes in there, and fried the amp, and then flipped it to cut his losses. Report him for sure.
A 2:100 is a newer amp too. He totaly beat the hell out of it. It's not a total loss though. If all' that's wrong with it is a screen resistor, then repairing it isn't major. A blown screen resistor is a very common thing in a tube amp, but not because the tube was jammed in the socket the wrong way. :roll:
I wouldn't be to hung up about using the exact replacement for a screen resistor. But if you can wait, I'm sure you can get them from Mesa if you can't find them in stock somewhere else. But the blue metal film flame proofs would be just fine, and they're cheap and readily available.
If your comfortable doing the repair yourself do it yourself. According to the schematics I've seen it's a 1k 2 watt resistor. The resistor is pretty standard across the dual rectifier brand. If you want to be certain of the value measure the other resistors with a multimeter. Remember that there is a 5-10% variance allowed on the resistor value. Meaning they can measure anywhere from 900 ohms, to 1.1k. The brand shouldn't make a difference. Get a decent quality resistor and you should be fine.
mikeymike
Well-known member
msi said:
Yeah I'm thinking about just buying one. I wonder if radio shack will have 2 watt resistors though. The one near me sucks. Hey do you think you can tell me where I can find that schematic? I have a couple schematics of different mesa amps but not the 2:100. Do you think I could look at the dual recto schematic since they claim the 2:100 is two DR power amps? I want to make sure a 1k ohm 2watt resistor is the right one before i go buy one. Thanks man.
mikeymike
Well-known member
RobertH said:
I'm not an amateur when it comes to electronics. Or are you saying this thing is so messed up it could kill me?
No I don't think it's that messed up, but the fact that you couldn't tell for sure if that was a resistor or not leads me to believe that you may be getting a bit over your head. This isn't a transistor radio, it can hold some pretty ugly voltage inside if not dealt with correctly and instead of a simple fix that would take a qualified tech about twenty minuets to perform you'll end up possibly having a really bad day. Just looking out for ya. :wink:
mikeymike
Well-known member
RobertH said:
I was pretty certain it was a screen grid resistor before I ever posted. I have soldered many things and I have worked around plenty of capacitors that would make the ones in a 2:100 look like watch batteries. De-soldering the resistor and putting a replacement one in is not a feat. People who try to tell others 'you probably can't do this' are whats killing creativity. Anyone can do anything if they want to. I know not to fool around with the high voltage/amperage caps and to keep the amp unplugged when working on it. How did your post truly help me? Just because I'm not familiar with what the resistor does doesn't mean I can't replace it safely and properly. I have quite a bit of soldering experience under my belt just not on tube amps. Thanks for looking out for me though. If you want to help you could tell me more about what the resistor does for the screen grid and what happens to the amp when it's used when the resistor is blown. It still sounds decent and i'm wondering what could have happened when this guy played the amp with a blown resistor over a long period of time.
Thanks though for trying to keep me from killing myself but I can handle this.
mikeymike
Well-known member
RobertH said:
Any ideas about what happens to the tube or amp over time when the resistor is popped?
timv
Well-known member
He wasn't trying to be a jerk and say stay out of there but since you posted you knew to stay away from high voltage caps but don't know that the one side of that resistor is connected to the high voltage, you might want to be very careful, unplug the amp and turn the power and standby switches to on and let it sit for several minutes, this will help drain the power....
With that resistor blown, that tube wasn't working anymore. It is easy to replace.
With that resistor blown, that tube wasn't working anymore. It is easy to replace.
timv
Well-known member
He wasn't trying to be a jerk and say stay out of there but since you posted you knew to stay away from high voltage caps but don't know that the one side of that resistor is connected to the high voltage, you might want to be very careful, unplug the amp and turn the power and standby switches to on and let it sit for several minutes, this will help drain the power....
With that resistor blown, that tube wasn't working anymore. It is easy to replace.
With that resistor blown, that tube wasn't working anymore. It is easy to replace.
mikeymike
Well-known member
timv said:
Yeah I guess I was being defensive. I did some reading and I discovered what the screen grid is for so I'm pretty much informed I suppose. It was under my impression that the screen grid excites the electrons to flow to the anode so without the screen grid functioning properly (the resistor is blown and no current gets to the grid) the tube is just LESS efficient. So I was just assuming that the tube wasn't working to it's fullest potential.
But you say it wasn't working at all, perhaps if a tube is designed with a screen grid the gap is too far for the electrons to jump across if there isn't a functioning grid? Maybe? Let me know more about what you know if you don't mind. Thanks for taking the time to answer. I also found the schematic for the 2:100 and I did see the voltage going across is over 400 so I am careful in that regard.
