so today i was going to play my 2 channel mesa dual like usual. i turned it on, left in on standby for maybe 10 minutes tops. i came back into my room and switched the power on and the second i did i heard what sounded like a hissing noise and smelled something burning. the amp immediately shut off on its own and wouldn't turn back on. i checked and the fuse was blown obviously. does anybody have any idea what could have caused this and also how much damage i'm looking at here? burning smells and not working amps is not sounding too good to me... help :/
well.. i think i'm screwed here...help again please :/
- Thread starter coryxcfc
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Jerrick said:
+1
If the amp blows fuses when coming out of standby it is most likely a power tube issue. If the amp blows a fuse as soon as it is powered on, it may be a rectifier tube issue.
A blown grid resistor is an easy fix, especially for a certified tech.
Do you have spare fuses and power tubes?
Dom
That happend to me once and, you could see this orange flash on the wall of the tube blowing out, and the amp shut off immediately.
Luckily it was only a blown power tube, no grid resistor. I like to put a mirror behind my amp on the wall to keep watch over the tubes, AI, one red plating of something else like that.
Luckily it was only a blown power tube, no grid resistor. I like to put a mirror behind my amp on the wall to keep watch over the tubes, AI, one red plating of something else like that.
i just replaced all of the tubes though in January. do you guys think that it would blow that fast? and how can i check to see which tube is the one thats blown? and if i did blow a grid resistor how much would that be to fix approximately? thanks for all the help again you guys this forum is like a godsend to all mesa players!
coryxcfc said:
I ordered a new set of power tubes, cleaned all the contacts and everything, put them in, played on them for about an hour, sounded great. The next day, 15mins into practice, one red plated on me.
One way to tell, is if they have a logo on the tube, and the tube red plates, it gets so hot that the logo will discolor and be a lot darker than the other logos on the good tubes.
Prices will vary, around here, the few techs I know will do something like that for around $10. Ive heard of some people paying closer to $20-$20 though. Most tech will know what you are talking about and give you an estimate, so id call around a little.
clutch71
Well-known member
coryxcfc said:
Yes tubes can blow that quick....they are not made like they used to be. What I would recommend is that you retube the power section and replace the blown fuse. Fire it up and pay attention to the gain. You'll know if a grid resistor is blown if your gain is greatly reduced. BY this you will need the gain dimed to achieve what you would normally get on noon/ 1 o'clock.
Mesa tubes are plug and play.
94Tremoverb
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You may not know a grid resistor is blown if it's just one - in a 4-tube amp, that would leave three tubes running which still produces a nearly symmetrical waveform and unless the amp is really working hard can be difficult to tell the difference.
The best way to check is to run the amp with only *one* power tube - this is quite safe, although it won't sound good at anything over very low volume because it will give only a half-wave output - but if it makes sound at all, the grid resistor is definitely not blown (although it could be stressed and a bit out of spec, possibly). Go through all four tube sockets in turn with known good tube(s).
Unfortunately tubes can fail at any time without warning, from brand new onwards - in fact, they are probably *more* likely to fail after a short time than once they have been effectively tested by running in the amp a while. But they can still fail when they're old too. Always keep spare tubes and fuses.
It's worth keeping the good tubes from the old set as your spares - you can identify the bad tube if you have spare fuses too, although there is still the small risk of frying the screen resistor if you do. Simply test one tube at a time until the fuse blows. If it doesn't blow with any of them, you have a tube with an intermittent short... which is a pain! You can also sometimes tell by looking at the tube, although not always. Look for things like extra silvering on the inside of the glass in places where it shouldn't be, or 'watermarks' (actually burn marks, but they often look like water stains) on the grey plate structures.
The best way to check is to run the amp with only *one* power tube - this is quite safe, although it won't sound good at anything over very low volume because it will give only a half-wave output - but if it makes sound at all, the grid resistor is definitely not blown (although it could be stressed and a bit out of spec, possibly). Go through all four tube sockets in turn with known good tube(s).
Unfortunately tubes can fail at any time without warning, from brand new onwards - in fact, they are probably *more* likely to fail after a short time than once they have been effectively tested by running in the amp a while. But they can still fail when they're old too. Always keep spare tubes and fuses.
It's worth keeping the good tubes from the old set as your spares - you can identify the bad tube if you have spare fuses too, although there is still the small risk of frying the screen resistor if you do. Simply test one tube at a time until the fuse blows. If it doesn't blow with any of them, you have a tube with an intermittent short... which is a pain! You can also sometimes tell by looking at the tube, although not always. Look for things like extra silvering on the inside of the glass in places where it shouldn't be, or 'watermarks' (actually burn marks, but they often look like water stains) on the grey plate structures.
