EVH 5150 just took a crap

  • Thread starter Thread starter ledvedder
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ledvedder

ledvedder

Well-known member
I was playing the 5150 earlier and everything sounded fine. Then, I started hearing this buzzing from the speakers. After about 10-15 seconds, the amp shut off. I pulled the fuse out of the back, and it's fried. What do you think it could be? Tubes? Something else?
 
Pull the power tubes and replace the fuse. Turn it on with no power tubes. If it blows another fuse it’s something other than the tubes. It’s a good chance you have a bad power tube though.
 
I ordered the fuses on Amazon, but they won't be here until Tuesday.
 
LP Freak said:
Pull the power tubes and replace the fuse. Turn it on with no power tubes. If it blows another fuse it’s something other than the tubes. It’s a good chance you have a bad power tube though.
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Yep
 
ledvedder said:
Would there be any visible signs on a bad 6L6?
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Sometimes you can see the vacuum broken. It will be obvious because the gas will have colored the exterior. But there are other things that can go wrong with the tube that won't be visually apparent
 
Home Depot/Lowes only have 2, 3 and 5 amp fast acting fuses. This requires 4 amp. Pretty annoying.
 
Typically for a PV5150 you'll use something in the range of 0,25amps to 0,5amps ceramic "slow blow". I have these in my Payyvvay 5150 II and my two Diezel Bad Boy's. :cool:
 
You need to check your screen grid resistors. You can do this in circuit with a multi meter. If one is bad you might have the same issue depending if it was tube related.
 
glip22 said:
You need to check your screen grid resistors. You can do this in circuit with a multi meter. If one is bad you might have the same issue depending if it was tube related.
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I have a multi meter. Can you explain how to check them?
 
I'm not sure of the 5150's layout. The old ones had the resistors under a separate PCB. They should be right where your power tubes plug in underneath. You can find the traces and touch your meter probes to both across the resitor. Set meter to ohms. I think these are 6L6. You should read 820 ohms approx. . If it's EL34 set to Kohms and read 1K. They could have changed to 1K on either 6L6 or EL34. I'm not sure on that. If you don't get a reading or the reading runs away one is probably shot.
 
There is a fuse on the actual pcb. You need to take the chassis out to check.
 
First off, there are both fast and slow blow fuses. fast on the mains side which has to be AC rated, and slow on the secondary side that’s DC rated. Follow the fuse guidelines for the external mains and DC secondary fuses.

The screen grids can get damaged when a power tube shorts. The screen grid resistors are on the power tube board mounted upside down and are not easy to check like a Marshall. First you’ll need to unplug the amplifier from the wall and assure the HT and screen capacitors are fully drained. Verify it’s zero volts with a DC multimeter. You’ll need to unplug all of the power tubes and unplug the power board. you’ll need to measure across pins 3 and 4 and see if the resistance is 100 ohms. If you don’t get 100ohms and get open, a screen grid resistor was damaged and you’ll need to pull the board to check the traces and replace the resistor with a 5W ceramic resistor.

There are lethal voltages in an amplifier even if it is unplugged and turned off. If you arent comfortable with working on it then take it to a tech.

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glip22 said:
You need to check your screen grid resistors. You can do this in circuit with a multi meter. If one is bad you might have the same issue depending if it was tube related.
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This x1000. I’m more than certain you have one or more bad screen resistors. The bad part is that you have to drill out rivets to get to them. I’ve done it before and it’s a total pain in the ass. I’ve increased the value on the resistors a little bit to provide more protection to the tubes. Changing the values does change the tone a little bit, but it never bothered me much since I always use a pedal out in front of a 5150.
 
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