Members MakuseruSukotto Posted November 7, 2009 Members Share Posted November 7, 2009 Ok, so I have an Ampeg R50H, and last week I was playing it and all of a sudden I got no volume. So I figure "ok, maybe it's tubes" so I changed them all, still nothing. So I pulled the chassis out, and two resistors (R44 and R46) looked pretty bad. R44 is coming off of one of the pins of a power tube, its a 470? 5A ceramic resistor. From the top I could see something was wrong, it is discoloured white in the middle with black around that, and a crack in the very middle of the white. So I pulled it off and measured it with a multimeter, and it didn't read anything, so it defiantly is dead. R46 is on a separate board, It's a 470? 5W metal oxide resistor. the board that this resistor on has blackened considerably (no broken traces) looks like it got really really hot. So I figured that resistor went out as well, but when I pulled it off, it looked fine. Measured it, it read 466?. There is only a slight discolouration (its lighter than the rest of the resistor) on the bottom of it. Is it just getting so hot its burning the board, without the actual resistor going out? http://www.schematicheaven.com/ampegamps/ampeg_r-12r_212r_50h_reverbrocket_ri.pdf Here's a schematic. Would the first resistor going out cause the second one to heat up or anything like that? Link to comment Share on other sites More sharing options...
Members mrbrown49 Posted November 7, 2009 Members Share Posted November 7, 2009 I suspect your bias and power tubes are screwed up causing the components to over heat. You should check that. I had a similar problem when a set of power tubes had a meltdown on my sr212rt. Link to comment Share on other sites More sharing options...
Members MakuseruSukotto Posted November 8, 2009 Author Members Share Posted November 8, 2009 I suspect your bias and power tubes are screwed up causing the components to over heat. You should check that. I had a similar problem when a set of power tubes had a meltdown on my sr212rt. That was my first thought as well. Do you know where I can find this ceramic resistor? I cant seem to find one. The part number on it (I assume thats what it is) is N IRC 0037.And below that it just says 470?10% PW-5A I tried searching those paramaters on Mouser, but the closest thing I found was this. And I don't think that's right. Link to comment Share on other sites More sharing options...
Members drewl Posted November 8, 2009 Members Share Posted November 8, 2009 Without looking at the schematic, I'm guessing that being 470ohms, they're the screen grid resistors on pin 4 of the power tubes, Fenders or most 6L6 amps use 470ohm, marshalls and EL34's use 1Kohm.it's a common occurance meaning the output tubes are biased too hot or they are bad.You'll often see them replaced on any amp that's been in use for a while.Fender usually used 1 or 2w carbon while Marshall used the ceramic 5w. Link to comment Share on other sites More sharing options...
Members mrbrown49 Posted November 8, 2009 Members Share Posted November 8, 2009 That was my first thought as well.Do you know where I can find this ceramic resistor? I cant seem to find one.The part number on it (I assume thats what it is) is N IRC 0037.And below that it just says 470?10% PW-5AI tried searching those paramaters on Mouser, but the closest thing I found was this.And I don't think that's right. I'm not sure where to get them as I had mine fixed up by a tech. It wasn't very expensive to have done, the new tubes were the pricey bit. He did install them a ways off the board so that if they do burn up again they won't do as much damage to the board. I'd encourage you have yours checked over by a tech just to be sure that everything else is working properly. Link to comment Share on other sites More sharing options...
Members syscrusher Posted November 8, 2009 Members Share Posted November 8, 2009 Ok, so I have an Ampeg R50H, and last week I was playing it and all of a sudden I got no volume.So I figure "ok, maybe it's tubes" so I changed them all, still nothing.So I pulled the chassis out, and two resistors (R44 and R46) looked pretty bad.R44 is coming off of one of the pins of a power tube, its a 470? 5A ceramic resistor. From the top I could see something was wrong, it is discoloured white in the middle with black around that, and a crack in the very middle of the white. So I pulled it off and measured it with a multimeter, and it didn't read anything, so it defiantly is dead.R46 is on a separate board, It's a 470? 5W metal oxide resistor. the board that this resistor on has blackened considerably (no broken traces) looks like it got really really hot. So I figured that resistor went out as well, but when I pulled it off, it looked fine. Measured it, it read 466?. There is only a slight discolouration (its lighter than the rest of the resistor) on the bottom of it. Is it just getting so hot its burning the board, without the actual resistor going out?http://www.schematicheaven.com/ampegamps/ampeg_r-12r_212r_50h_reverbrocket_ri.pdf Here's a schematic.Would the first resistor going out cause the second one to heat up or anything like that? Sounds like your tubes went bad, lost bias or shorted screens. When that happens, they pull a lot of current across the screen resistors and that R46 which is also supplies power to the rest of the amp. I always insist on using 1k screen resistors just to keep the voltage down just enough. Tubes these days just can't take the abuse. When I need fast parts right away, I go to this guy. Hoffman Amps Mouser part number is this 470ohm wire wound power resistor Link to comment Share on other sites More sharing options...
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