Amp volume fades in and out

jtcnj said:
Good luck, hope you get it sorted easily. Remember - safety first!

If you end up trying new power tubes:
As @syscokid reminded me, the Sovtek 5881/6L6WGC is not a 30w 6L6, but 23-26w depending on where you look.
Bias accordingly.

I mistakenly biased mine based on 30w max and ran it for quite a while with no ill effects before re-biasing based on 23w.
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I always bias with an O scope, and never have those problems.
The wave form shows the correct bias point, no matter what tubes are used.

You guys get a scope, and cut your bench time by 60% ! All the amps will bias just right, and confirm proper operation / clean power output every time....in half the time.

I think there might have been a problem with the bias, from the factory, in certain 5150 amps.
 
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syscokid said:
Ditto!
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LiveeviL2000 said:
My 5150 has had the volume fade out and come back a couple of time now.
I tried researching probable causes and the internet is full of possibilities. Most point to power tubes over heating, but there are a dozen other things that are suggested.

The volume fades out after a good 20 - 30 minutes of the amp being turned on. The after a minute or two it comes back.

Any help will be welcome
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I would:
Pull the tubes and clean the tube pins as well as the tube sockets.
Confirm there are no dirty pots by turning all of the controls starting at ccw to full cw without any guitar or cord plugged in.
If you are comfortable with opening up the amp (safety first) pull the cabinet and make sure you re attatch the speaker then use a wooden chopstick or popsicle stick and gently push on each component on the board. Remember SAFETY FIRST and one hand in your pocket. If there are cold solder joints or bad components this might help you find the issue. If you have never done this it might be better to take it to someone you trust. Wood does not conduct electricity, however I can’t emphasize enough that this is very dangerous and that even when powered down capacitors can store 450 to 500 volts even with the power off.
 
MarkA said:
I would:
Pull the tubes and clean the tube pins as well as the tube sockets.
Confirm there are no dirty pots by turning all of the controls starting at ccw to full cw without any guitar or cord plugged in.
If you are comfortable with opening up the amp (safety first) pull the cabinet and make sure you re attatch the speaker then use a wooden chopstick or popsicle stick and gently push on each component on the board. Remember SAFETY FIRST and one hand in your pocket. If there are cold solder joints or bad components this might help you find the issue. If you have never done this it might be better to take it to someone you trust. Wood does not conduct electricity, however I can’t emphasize enough that this is very dangerous and that even when powered down capacitors can store 450 to 500 volts even with the power off.
Click to expand...

Yeah. I’m not an amp guy like I said in one of the beginning posts.
That’s not something I feel comfortable with.
Right now it seems to be ok. It hasn’t done it since I unplugged everything and plugged it all back in.
If it does it again, then I’ll take it to a local amp shop here and have them look at it and even bullet proof it for me.
 
LiveeviL2000 said:
Yeah. I’m not an amp guy like I said in one of the beginning posts.
That’s not something I feel comfortable with.
Right now it seems to be ok. It hasn’t done it since I unplugged everything and plugged it all back in.
If it does it again, then I’ll take it to a local amp shop here and have them look at it and even bullet proof it for me.
Click to expand...
I’m happy to hear it working for you right now. I do a lot of tube amp / radio repairs and safety is always the number one priority. Take care
 
LiveeviL2000 said:
Yeah. I’m not an amp guy like I said in one of the beginning posts.
That’s not something I feel comfortable with.
Right now it seems to be ok. It hasn’t done it since I unplugged everything and plugged it all back in.
If it does it again, then I’ll take it to a local amp shop here and have them look at it and even bullet proof it for me.
Click to expand...
What is this?…sensibility? ;) …good stuff…having a sense of these things. Better for you to know your zone. I hope this turns out fine for you sir.
 
I would agree with a lot of the good advice here already. Volume cutting in and out is almost always power tubes failing or getting weak.

A good spray of Deoxit on every input and output jack/terminal is always a good idea as well
 
Amp Mad Scientist said:
I always bias with an O scope, and never have those problems.
The wave form shows the correct bias point, no matter what tubes are used.

You guys get a scope, and cut your bench time by 60% ! All the amps will bias just right, and confirm proper operation / clean power output every time....in half the time.

I think there might have been a problem with the bias, from the factory, in certain 5150 amps.
Click to expand...
I had to send back two EVH 5150 amps new, to get the third one sent that actually worked properly. The first amp new, no output at all. Everything was lighting up as if normal operation, but zero output, zip, zilch, nada! Amp two, big dent on the front of the amp cabinet right where the 5150 badge on front is located, plugged it in, got light no sound, zip, zilch, nada...third amp was gold..everything perfect and sound is frigging fantastic.

I was on a budget to purchase amp for $1,000.00 or less, had crossed out new Fender line of amps for many well founded reasons, and already own Fender 100 2x12 BUT wanted a tube amp. I'm not located close to retail stores and I don't drive currently due to health/medical reasons. Every time I was at Guitar Center, an angry customer would come into the store very pissed off at his Fender amp that just took a dive. One trip several customers were in a line with bad Fender amps! WTH! reason is Fender tossed cheap stuff in the build of their amps. How do I know if EVH is Fender or not? It is..but then it's not! Amp tech explained what EVH has that Fender does not in the amps. I was already not going to purchase anything new Fender tube. I got lucky with the EVH, super happy with it.
 
LiveeviL2000 said:
OK the weirdest thing, I unhooked everything. Then hooked the amp up to only my Randall cab, I've been playing and noodling for almost 3 hours and the sound hasnt faded.
Could it have been the Carvin cab? or maybe the combination of the two cabs?

I don't get it.
Mind you if that is the fix, I'm not complaining. Just weird.
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You shouldn't have played the amp without taking all the readings first.
The worst thing you can do is
turn it back on and "see what happens."
Troubleshoot FIRST, find the problem, correct the problem, put the tubes in LAST.

You asked for a tech, you ignored everything the tech told you.
That's what makes repair shops $$$ rich.

(you could have had $500 worth of help for FREE)

When your amp goes up in smoke, when your output transformer becomes a paperweight...when your output tubes are destroyed...
I hope you have much happiness.

If you are reading this post, trying to fix a 5150 amp: (above) is the perfect example of WHAT NOT TO DO.
 
Good on you taking the consideration of someone else doing it sometimes! That stuff ain't easy and is beyond me as well lol I did repair a few things once on one of my amps but it took some work and I lot of cursing when I messed up.

Something I might suggest if it DOES happen again? Is to have whoever you trust to work on it, check your bridge rectifiers. This same thing your describing happened to me on two different Marshalls and each time was a bad bridge rectifier and heat related. One would knock out the volume until I reset the amp ( SLX) and the other toasted the volume entirely (DSL50). Not saying this is exactly the issue for you? But food for thought!
 
Amp Mad Scientist said:
You shouldn't have played the amp without taking all the readings first.
The worst thing you can do is
turn it back on and "see what happens."
Troubleshoot FIRST, find the problem, correct the problem, put the tubes in LAST.

You asked for a tech, you ignored everything the tech told you.
That's what makes repair shops $$$ rich.

(you could have had $500 worth of help for FREE)

When your amp goes up in smoke, when your output transformer becomes a paperweight...when your output tubes are destroyed...
I hope you have much happiness.

If you are reading this post, trying to fix a 5150 amp: (above) is the perfect example of WHAT NOT TO DO.
Click to expand...
WTF?
Pretty passive aggressive.
Took it to a tech (Fauch). They are very good.
Everything checked out.
Amp is fine. Cab is fine.
$50 later. Peace of mind.

I appreciate your input and time, but I think you need to tone it down a bit. No need to get all worked up.
 
Naked Strat Brat said:
I had to send back two EVH 5150 amps new, to get the third one sent that actually worked properly.
Click to expand...
TTR member @Inspector #20 recently worked at the Fender facility in Corona, Crazyfornia. For a few months we all got to see some interesting manure behind closed doors. Follow the link, and go right to post #3… It should make you feel better…

Fender Amp Woes:

Affects the '64 hand wired Princetons too.
www.thetonerooms.com
 
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