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Old 03-03-2013, 03:56 PM   #1
R45VT
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General Amplifier Trouble shooting. No sound and odd noises.

General Amplifier trouble shooting. This is not for design concerns!


Table of contents
Post I: Generic Symptoms and Troubleshooting
Post II: No sound
Post III: Odd noises
Post IV: Further reading/photos of what can go wrong inside an amp

Symptoms of worn/defective tubes:
The easiest is the visual- if you see the silver coating(getter) has turned white it means air has entered the tube and it is defective.

-Microphonic


-Squealing


-Distortion and loss of tone

-Lack of EQ control- no matter how high or low you turn your treble knob it just isn't happening?

-Hum through speakers

-Loss of volume/headroom

-Crackling


-Red-plating



Symptoms of Capacitor concerns
Electrolytic causing popping. This guy was an idiot and used a metallic screw driver which is not recommended in a live amp !!!


Filter capacitors leaking causing motor boating


Generic troubleshooting

Disclaimer: Tube amplifiers contain lethal voltages inside their chassis, well in excess of what your body can handle. If you are not skilled in this area do not take a chance with your life. Amplifiers can store this lethal charge for an extended period of time even after being unplugged, do not open it up and poke around. If you are out of your league take it to an amp tech and live another day.

If you must open up your amp to inspect something please only touch things with a wooden pencil or chopstick and stick one hand in your pocket. Two bare hands touching the inside of an amp can kill.


- Have you tried another guitar?
- A different cable?
- Have you tried plugging directly into the input without any pedals?
- Is it a head with separate cabinet? If yes, do you have a speaker cable and not an instrument cable?
- Have you tried a new cable between the head and cab?
- Have you tried a different cab?
- Any sound if you wiggle the cable at the input jack?
- Have you check the speaker connection in your combo amp?
- Are you using a shielded instrument cable?(Check to make sure you are not using a TRS or speaker cable!!!)
- Have you tried tried using a different outlet?
- Are you next to noisy electrical devices such as microwaves?
- Lighting? Some types of bulbs are noisier than other try switching them off
- Have you tried a different power outlet?

Last edited by R45VT : 03-13-2013 at 02:28 AM.
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Old 03-03-2013, 03:57 PM   #2
R45VT
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Part I: No sound

Does the amp turn on? (If no check main fuse, the filament should not be broken and sometimes this may not be easy to tell. Always replace with the same amperage and make sure its the correct speed; fast or slow blow)

*It should be noted fuses blow for a reason. Power tubes are the most common cause of blown fuses. It may or may not blow right away.

**HT fuses are often located inside the chassis of an amplifier.


Yes the amp turns on:

Is the speaker plugged in?

Do you have an FX loop? (If yes plug your guitar into the FX return and see if you have sound) If yes there is sound then you have a preamp concern. If no you are looking at your power section.

No sound out of the preamp: Have you swapped preamp tubes if in the preamp section? (More than 1 might be defective)

No sound out of the power section: Have you installed new power tubes and/or looked for blown HT fuse? Do any of the tubes show discoloration on the glass?

Past this point you might want to be thinking about taking it to a tech. If your guitar sounds through the FX return and you have installed new preamp tubes you could have a bad coupling capacitor. If you don’t have a soldering iron take to make friends with your local amp tech.
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See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.

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Old 03-03-2013, 03:58 PM   #3
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Part II: Noises

AM/FM coming through amplifier: Do you have your preamp tube shields installed? If it is still there you can try a choke on your mains cable, try using a different outlet. The most critical pieces inside an amplifier are more design concerns, the first gain stage and input. Bad routing/shielding or poorly designed screen grid value can easily contribute. See if others with the same amplifier are having the same concern.

Crackling, Popping: faulty cables, tubes, tube sockets are the most common cause. More in-depth concerns could be internal to your amplifier such as a capacitor. First off swap your cables and don’t forget your speaker cable! Next is the “tap test” for your tubes/valves. With the amplifier on and speaker connected take the eraser end of a pencil and tap on each one of the tubes one at a time. If you hear the tap coming through the speaker your tube have gone microphonic. If you hear a crackle then you need to clean your tube sockets. Deoxit is available at your local electronics or computer store. Spray the pins of your tubes(after they have cooled) and never spray into your tube sockets. Next wiggle the tubes around in the socket in a circular motion. Let the deoxit dry for a few minutes. Repeat the test. If the crackling persists you might need to have your socket replaced.

Squealing: start by changing your preamp tubes. More than 1 might need replacing.

Noises when turning knobs: some amplifiers are notorious for having scratchy pots. When you turn the know you hear a static type noise come through. Sometimes the pots can be cleaned with a can of compressed air for removing dust. If it continues or you can’t access the potentiometer then it will need replacing.

Steady Hum with no guitar sound: are your tubes red plating? This is typically a symptom of failed power tubes. If they(the plates) are glowing red turn your amp immediately.

Loss of volume Lots of issues can cause this. First off- tubes- pre and power tubes. Internally faulty potentiometers or cracked solder joints are also common.

Reverb acts as tone knob Was any recent work performed that required removal of the reverb tank? Was it tightened to much? It should have movement on the isolators. Also give it a good hit to make sure its not stuck. Retest operation.

Past this point you might want to be thinking about taking it to a tech. Crackling and random noises can be from many sources, including cold solder joints. If you hear a popping noise when powering on or off if could be a capacitor discharging somewhere inside your amplifier. Most techs can isolate the noise in no time at all and have you back to playing your Metallica cover tunes in no time.

Last edited by R45VT : 03-29-2013 at 04:06 PM.
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Old 03-03-2013, 04:13 PM   #4
R45VT
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Some further outside reading

Troubleshooting
http://www.geofex.com/ampdbug/ampdebug.htm

http://www.premierguitar.com/Magazi...ooting_101.aspx

http://www.sweetwater.com/sweetcare...shooting-guide/

Preamp tube shields
http://www.rig-talk.com/forum/viewt...t=47465&start=0

http://www.thegearpage.net/board/ar...hp/t-27710.html


What can go wrong internally

Again lethal voltages can be present even after the amplifier is unplugged for extended periods of time. Do not attempt to open your amplifier up if you are not qualified. If you must open up your amp to inspect something please only touch things with a wooden pencil or chopstick and stick one hand in your pocket. Two bare hands touching the inside of an amp can kill.

Cracked solder joints


Overloaded fuse clip- see the discoloration on the PCB below the fuse clip?


Loose connections- see clear connector on the left switch?


Burned resistor


Burned connector (a la the famous Bugera 333XL)


Worn out channel switch
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Quote:
Originally Posted by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.

Last edited by R45VT : 03-04-2013 at 10:58 PM.
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Old 03-03-2013, 04:39 PM   #5
R45VT
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Reserved for foot switch concerns.... info and pics to come.

Last edited by R45VT : 03-13-2013 at 02:38 AM.
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Old 03-03-2013, 04:40 PM   #6
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Reserved for pictures and videos.



And beer.
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Originally Posted by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
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Old 03-03-2013, 04:41 PM   #7
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Originally Posted by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
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Old 03-03-2013, 04:51 PM   #8
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Originally Posted by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
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Old 03-03-2013, 05:07 PM   #9
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that should prob be enough reserves.

maybe we should split this into at least 3 parts. the first part can be the basic troubleshooting, that will consolidated certain repeated advice (like 'make sure you are using the right cable' by creating a small cable inspection/QA/troubleshooting list).

Part I trouble shoot

Part II Amp makes no noise

Part III Amp makes noise.

?

maybe even one post for each part, that way you can expand the lists easier. i can see more and more content expanding this thread.
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Old 03-03-2013, 05:45 PM   #10
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^ I would actually put Troubleshooting last with a disclaimer that tube amps can be dangerous.

I like the symptoms first/troubleshooting second approach
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Old 03-03-2013, 05:53 PM   #11
R45VT
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I will work on resizing the pictures.

If anyone else would like to make suggestions or is confused on anything please ask or point something out. Thanks!
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Originally Posted by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.

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Old 03-04-2013, 12:30 AM   #12
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Good thread! Deserves a sticky.
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Old 03-04-2013, 05:45 PM   #13
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i see some formatting has been implemented. this has a cleaner flow.

i like how you bolded symptoms for quick lookup. plus the videos demonstrating common symptoms is a nice addition.

have you happened to contact anyone like cath to see if we are forgetting anything obvious?
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Old 03-04-2013, 05:48 PM   #14
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Cath is sick right now. Maybe the bump will help get some others eyes on it.

I will add a few off topic items like footswitch concerns, noises from household wiring.

It won't be today. Busy day on my end.

If anyone would like something added or see room for improvement please let me know!
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Originally Posted by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
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Old 03-04-2013, 05:52 PM   #15
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Looking better all the time. I removed my post 5.
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Old 03-04-2013, 06:05 PM   #16
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Also, one minor typo and suggestion:

Amplifiers can store this lethal charge for an extended period of time even after being unplugged, so do not open it up and poke around. If you are out of your league take it to an amp tech and live another day.

If you must open up your amp to inspect something please only touch things with a wooden pencil or chopstick and stick one hand in your pocket. Two bare hands touching the inside of an amp can kill.
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Old 03-04-2013, 06:40 PM   #17
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In addition to placing it at the beginning, I'd make the font on the disclaimer larger.

'so' isn't necessary after the comma.

Not sure I agree with the AM/FM part in regard to removing cables. Removing the antenna from a radio makes it not pick up signal any more either, but it's still a radio...(Open to being corrected, of course)
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Old 03-04-2013, 07:43 PM   #18
R45VT
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I updated those items. Maybe we can get some more feedback on the AM/FM. From what I gathered a bad design/execution contributes the most rather that a failed component, aside from a failed input grid stopper. I'll try to expand that with some research and external links.

I will remove the guitar/cable portion as that should have been ruled out earlier.
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Quote:
Originally Posted by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.

Last edited by R45VT : 03-04-2013 at 09:25 PM.
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Old 03-04-2013, 09:21 PM   #19
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One of the most common problems I've had with amps was bad solder joints on the pots and jacks. Symptoms include crackling, popping, hiss build up till it pops, and most notably volume drop-outs and fading as the amp heats.
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Old 03-04-2013, 09:24 PM   #20
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Quote:
Originally Posted by fly135
One of the most common problems I've had with amps was bad solder joints on the pots and jacks. Symptoms include crackling, popping, hiss build up till it pops, and most notably volume drop-outs and fading as the amp heats.


Good point and thanks. I will work it in a little more.






Anyone up for preamp shield discussions? Some are grounded and some aren't- I would assume it would need to be grounded for suppression? Thoughts?
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Originally Posted by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.

Last edited by R45VT : 03-04-2013 at 09:25 PM.
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