#1
Hey, I was wondering if anybody can help me with changing valves on a tube amp, or point me to a site that can.

I've got a Vox AC15, and it's only been four months but annoyingly already one of the valves seems to be going - I'm getting a harsh crackling noise then a hum. It's been getting more and more frequent as I've been playing and I know I have to change the valve now as it's practically unusable otherwise.

I want to know what equipment I need, what I should do to test the valves, and what precautions, etc. I should take when changing them. I can't really afford to take the amp to a professional as I'm a student, and have very little money at the moment.

Any help would be greatly appreciated.

Thanks
#2
Sounds to me like a bad cable or bad input jack on either the guitar or amp

if you do not know what you are doing when changes valves, get a pro to do it, you can seriously damage your amp and possibly injure yourself...they hold a charge even when not plugged in
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#3
^ Tubes don't. The capacitors do. As long as you're not messing around INSIDE the amp, you should be fine. I really wish people wouldn't say completely false things and scare people unnecessarily. You shouldn't need anything besides new tubes to change the tubes. As far as testing them, you look for a couple things. First, is one glowing a different color than the others? Is it getting little spark flares or glowing purple? Something that shows a vacuum leak? Also, with the amp on, tap the tubes with a pencil. Do you hear a noise? Those are really the only ways to find a bad tube without a tube tester, which is expensive.

As far as changing them, tubes just pull right out. It's easier than changing a light bulb. When replacing power tubes, always replace both. And make sure to buy a matched set. That way, you'll still get good efficiency even if you can't afford to get your amp rebiased. If it's a preamp tube problem, you can just replace those individually without any other concern.
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Last edited by Dirk Gently at Sep 27, 2007,
#4
Turn your amp on and tap the tubes with a pencil. Listen for noise.
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#5
I heard that if your tubes go bad the amp can shock you to death clear across the room.
You say its been four months. Is it still under warrenty? Tube warrenties are usually only good for 90 days, but if its something else you don't want to deal with take it to a shop that deals Vox.
#6
I've heard they have magical ninja powers and will kill you in your sleep once they turn bad.
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#7
^You may be right. I heard all the victims of the "Ninja Burglar" had tube amps. A lesson to tube amp owners. Treat the amp right or suffer the consequences.
#8
Thanks for the tips, Dirk, that's a great help.

I know it's not a faulty cable, etc., as it makes the humming and crackling whether you have anything plugged in or not.

My main problem is it's fairly difficult to access the tubes while the amp's on from what I can see, but I'll give tapping them with a pencil a go tomorrow. Should I take any precautions? Don't particularly want to get electrocuted!
#9
Also for future reference is there any way to identify what kind of tube is going wrong from the symptoms? Mine is a crackle and hum problem, and from what I've read, I assume that means it's pre-amp?
#10
I have a Marshall DSL 50 with two power tubes I change bare hand all the time, there is no chance of you getting shocked whatsoever, even if there was its only a 110/220 volt and 25-50 watts, the tube death shock is bull shi-t at its finest, that charge would never kill you even if you were to recieve a full on shock, if you really wanna be safe, before you change them, make sure the amps been off a power source for a few hours so whatever current they had can discharge.
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Last edited by DirtyDeeds at Sep 27, 2007,
#11
I know, I agree with you there. But would it not be dangerous sticking my hand in the back to try to tap the tubes with a pencil while the thing's on?
#12
^that's why ur using a pencil. not ur finger.
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#14
use the rubber eraser side so the electricity doesn't go through the pencil? never done it myself. I haven't changed mine yet, only got my amp last month though. Well since this question is somewhat related, does anyone know if if i'm supposed to take the back part off of my amp? it's like a cage looking thing so i can't reach the back part of the speakers or the tubes or anything.
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#15
^probably. on my JCM2000 i had to take off the back part to work with the tubes. (it was actually my reverb that had a problem, but same case.
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#16
Quote by ECistheBest
^probably. on my JCM2000 i had to take off the back part to work with the tubes. (it was actually my reverb that had a problem, but same case.

but do you have to keep the back on for normal useage? mine's kinda fallin apart but that's another story lol
my gear:
Jackson DKMG(the one with EMG 81/85's)
b-52 AT 212 100 watt amp
old gear i'll probably sell eventually:
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gunmetal grey Fender squire strat
Fender 65R amp
#17
lol i have mine kinda dangling... i need to put my screws back on lol.
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#18
Remember, you're talking about using a PENCIL. Wood does not conduct electricity. Neither does glass. And the reason you use a pencil is because it keeps you from getting burned and to give you extra reach. You won't get electrocuted tapping the glass with a pencil. Seriously. Don't overthink this.
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#19
^good point. but i wasn't the one overthinking.
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#20
All right, thanks, guys! I'm going to give it a go today. If I don't respond again you know what's happened to me.
#21
try another forum, 'Guitar Gear & Accessories', they have a thread on tubes and tube amps.
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#22
OK I had a go and a friend's given me a replacement pre-amp, which was nice of him, but the tubes are nigh on inaccessible. I assume I have to remove a part of the chassis, but I dunno where to start. Vox's site's utterly unhelpful. These things should come with manuals ...
#23
Quote by Dirk Gently
^ Tubes don't. The capacitors do. As long as you're not messing around INSIDE the amp, you should be fine. I really wish people wouldn't say completely false things and scare people unnecessarily.


Dirk you really should know what you are talking about before you say others are sayong false thing...YES you can get electrcuted from the tubes and YES they can hold a charge...also you pencil tapping thing....you don't use a pencil because you can get burned (yes you can gt burned but thats not why) You use a pencil cause you skin has oils on it that wil remain on the glass when you touch it (touch a mirror and see the print) anyway these oils can cause interuption in the electricity flow and also can caus ethe glas to crack wher ethe oils remain

AGAIN IF YOU DO NOT KNOW WHAT YOU ARE DOING WITH THE TUBES GET A PRO TO DO IT
BC Rich Mocking bird
Ibanez Artcore
Epiphone LP JR customized
80's Vantage
Takamine 12 String
Ibanez Bass
Washburn Bass
Marshall JCM900
Marshall 1960a 4x12 with 75's
Acoustic 150
Line 6 POD
Boss OC-2
Heil Talk box
#24
You don't know what you're talking about. I stand by that.

How the fuck do oils in your skin "interrupt the electricity flow" if they're on glass, which doesn't conduct electricity to begin with? The cracking issue can be a concern, but more on things like car headlight bulbs which use thin glass. I've been playing tube amps for almost 10 years and have never had a tube cracked because I've handled them. And I want proof of your assertion that tubes hold a charge after you turn the amp off, which is what "holds a charge" asserts. If you handle the tubes by just the glass, you CANNOT be electrocuted. It's physically impossible. Of course you should never directly handle tubes or any other part of the amp power circuit when the amp is on/plugged in. And when you're testing tubes with your finger, you can also use your fingernail.
Hi, I'm Peter
Last edited by Dirk Gently at Oct 1, 2007,
#25
this might have been said already but i Just wanna clarify something. Bad tubes relates to drops in sound volume, not crackling, sounds like a bad cable, or maybe a loose input jack
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#26
^ Not necessarily true. Tubes can crackle/get noisy ("microphonic") when they go bad.
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#27
Quote by thatguyaswell
Dirk you really should know what you are talking about before you say others are sayong false thing...YES you can get electrcuted from the tubes and YES they can hold a charge...also you pencil tapping thing....you don't use a pencil because you can get burned (yes you can gt burned but thats not why) You use a pencil cause you skin has oils on it that wil remain on the glass when you touch it (touch a mirror and see the print) anyway these oils can cause interuption in the electricity flow and also can caus ethe glas to crack wher ethe oils remain

AGAIN IF YOU DO NOT KNOW WHAT YOU ARE DOING WITH THE TUBES GET A PRO TO DO IT
...You're a jackass.

1) Valves don't hold a charge.
2) Maybe try washing, if you have enough grease on your hands to burn through glass then you have a problem.

Also, about the pencil, make sure you don't poke around too much with it because the lead is graphite and graphite is conductive... The valves aren't what you should worry about, just keep it away from anything live.
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#28
Quote by thatguyaswell
Dirk you really should know what you are talking about before you say others are sayong false thing...YES you can get electrcuted from the tubes and YES they can hold a charge...also you pencil tapping thing....you don't use a pencil because you can get burned (yes you can gt burned but thats not why) You use a pencil cause you skin has oils on it that wil remain on the glass when you touch it (touch a mirror and see the print) anyway these oils can cause interuption in the electricity flow and also can caus ethe glas to crack wher ethe oils remain

AGAIN IF YOU DO NOT KNOW WHAT YOU ARE DOING WITH THE TUBES GET A PRO TO DO IT


What a jerk. If what you said was true, surely thousands of pieces of glass would get smashed every time there was a thunderstorm.

And to MrCarrot, yes, there are probably better things than a pencil to poke around with. Use an old toothbrush or something.
#29
Quote by Dirk Gently
^ Not necessarily true. Tubes can crackle/get noisy ("microphonic") when they go bad.

hes right, i recently had a tube go microphonic. wow its was annoying. it was my first experience, so i took to the shop. they charged me for laber, those ****ers, if i knew it was a tube i would have just changed it myself.
#30
i have to say, i completely agree with dirk. this other guy doesnt know what hes talking about.

i will also say that valves do hold a charge, but your never going to be electrocuted through glass! however its not advisable to lick the prongs ( ).

that said, i never handle them using the glass, i use the plastic casing bit that runs around the bottom.