My 5150 is dead :( TUBE AMP GURUS HELP!!!!

guitarguru777

guitarguru777

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Nov 13, 2003
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My baby, My sweet darling, My HOLY SHIT YOUR 5150 SOUNDS AMAZING AMP is no more :(

Last night during band rehearsal the amp started making this odd noise. so i stopped then I heard a POP. I was like WTF, so I hooked up my Krank finished practice and decided to open her up this morning.

So I opened her up and lo-and behold its FRIED, I means FUCKED fried. Blown caps, blown fuses .... SHES FUCKED!

IMAG0195.jpg


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Any idea what could have caused this? I stopped running the KT88 / 6L6 combo MONTHS ago, and went to Sovtek 6L6WXT+ in the power section. Got them from Tube Depot so i doubt its a bad tube.....

Also as a amp tech any idea what the ball park cost to fix it is? Should I just buy another 5150 and bury this one at sea?

I am SOOOOO fucking heartbroken right now.
 
You can clean the "explosion" with some alcohol and check of the "track" on the pcb is damaged or not...and also the back side.
Did anything disappear? It seems some transistor exploded...or cap...?
 
Which caps popped? I didn't see anything visibly extruded besides the resistor in your pics.

In one sense you're lucky it happened this early on in the power stage. That resistor is only a 1/4W part so it would have acted like a fuse and taken the brunt of the current. Desolder the resistor. Clean the board with rubbing alcohol and see if any of the traces went too. If not it's salvageable with a little bit of work. Worst case, IIRC the main board is $300 from Peavey and they send it fully populated. If it's just the filter caps, rectifying diodes and fuses + sundry resistors you're looking at around $30 in parts.
 
guitarguru777 said:
I'm deathly afraid to stick my hand in there after all the horror stories I have heard about caps holding a charge :(
Click to expand...

sprack said:
Don't discharge those filter caps with a DMM. Leave it off and plugged in overnight. Check it with a DMM later.
Click to expand...

5150s have discharge resistors. I have taken mine apart and prodded around many times and never even received a mild shock. However because of the one resistor failure, you should check the diodes in the power supply (the rectifier). A DMM across each rail, would let you know that they are drained.

From Memory, the resistor that went is the +24Vdc pull up resistor on the 6.3V heater voltage. It is what elevates the heaters for the later tubes which require it. I am having a hard time though, determine how such component would burn out like that unless something in the heater line was somehow shorted to ground then yes I can see that resistor going. Could also be a manufacture fault on the tubes. If that's the case you would need to find where that short has taken place.
 
Don't go inside it if you don't know how to properly bleed it out(Despite what anybody might say on this forum.).
Sure, i doubt anything will happen to you, but if anything happens you're pretty much fucked.

Sprack.. if thats not a diode you may lube up my anus and tickle me with your penis.
 
Oh, and the traces are on the other side, so unless the resistor cracked the whole PCB, than they are intact. From the looks of it, the resistor just cough fire for a second from the heat and created a nice layer of carbon.
 
kaomao said:
I think after 1 day turned off, the amp is safe! caps won't hold current forever!
Click to expand...

Unless it has a built in bleed-out circuit it can hold the current for YEARS(Dangerous for weeks.).
 
kaomao said:
I think after 1 day turned off, the amp is safe! caps won't hold current forever!
Click to expand...

Notuern said:
Unless it has a built in bleed-out circuit it can hold the current for YEARS(Dangerous for weeks.).
Click to expand...

Yes, if the bleed off resistors did not work the caps can hold their charge for years. However the 5150s where designed in such a way that the bias and power to the switching transistors that power the Power/Standby LEDs are powered from the filter caps. This is why it takes about 10 seconds for the standby LED to turn off after you turn the standby on. If the bleed resistors had failed, the LEDs (both of them for that matter) would still be on even after the amp was turned off and after is was unplugged.

Still like I mentioned before, an easy way to test is to take a DMM, connect the ground probe to the chassis and run the hot probe across the diodes, if they read no voltage, then you are safe everywhere in the amp, simply because all the other high voltage caps run through the bleed resistors as well, if there was a break in the line that prevented the other caps from draining, the amp simply wouldn't work.

Considering that, is why I said measure the diodes, and if you are really paranoid, measure the other axial caps on the mainboard. In terms of lethal voltages, you would have to be purposely trying to get a lethal shock. The one thing that ends up killing people is because they have the amp plugged in, which means if they do discharge a cap and they are touching the chassis, the signal has a direct line to earth in which the cap will fully drain through you. On the other hand if you did not have the amp plugged in, you would act as a secondary cap and would share the voltage with the cap, meaning you would see around half the voltage and the current would be fairly less. It will still light you up and hurt like a mother fucker, but no, you won't die.

A quick read on electrical safety is all you really need, and some common sense. The reason that most electronics guys` particularly in business (and websites) say if you don't know what you are doing don't mess around with shit is because they are liable to be sued if someone gets hurt or killed. Its a liability thing so they make it look like its the most dangerous thing in the world to keep the non-electrically inclined from doing it.
 
I posted this on the Peavey forum as well and one of the Peavey techs said exactly what you said winter its a 24 bla bla resistor thats designed to take the hit if something goes wrong.

He also stated this is always caused by a bad tube usually one with a short in it. These are brand new Sovteks so I am wondering if I have any recourse against Tube Depot in this for sending me a tube that was supposed to be bench tested that was clearly not.

Thanks for the info. I still dont feel much better but at least if I take it to a tech i have some semblance of a clue as to what needs replacing.
 
Went over and read the thread. Still don't understand why everyone thought the blown component was a diode, do they realize how fucking hard it is to blow a 1N4001. Anyway, they also kept assuming that it was the power tube filaments as well, which is odd considering the filaments are all connected from the same rail. Which leaves me to ask, when did you put the NOS Ei tubes in and when did you put the 6L6WXT+ in there, and was each tube change before or after you blew the fuse two weeks ago? That would help you determine which tubes they are.
 
TheWinterSnow said:
Went over and read the thread. Still don't understand why everyone thought the blown component was a diode, do they realize how fucking hard it is to blow a 1N4001. Anyway, they also kept assuming that it was the power tube filaments as well, which is odd considering the filaments are all connected from the same rail. Which leaves me to ask, when did you put the NOS Ei tubes in and when did you put the 6L6WXT+ in there, and was each tube change before or after you blew the fuse two weeks ago? That would help you determine which tubes they are.
Click to expand...


The Ei Tubes have been in there since 2010, the 6L6WXT+ are 2 weeks old. The fuse blew 2 days after I put the new tubes in, but at the same time I was trying some funky things with the FX loop and figured that was the culprit since I didnt see any abnormal light coming from the tubes.

After replacing the fuse i ran the amp at a 2 hour rehearsal with no issues, that same night I had another rehearsal and blew the main power fuse of the amp while my little FX Loops shit was going on so I figured that was still the culprit.

2 nights ago at a rehearsal I made it through 2 hours with no issues. Then (while looking at the amp from the front) the inner tube on the right side lit up like a christmas tree. I immediately Stopped playing and went to power down the amp but no luck the resistor had blown by this point.

I do think its the power tubes as stated by the guys on the peavey forum. I doubt running an overdrive to color the signal a bit in the loop would cause something like this. Even the guys at Peavey stated the same thing.
 
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