how do i know when to change a tube

[motorboy29]

I really dont know anything about tubes/amps ect. except that if you f*ck with em you can fry the crap outta yourself even without it plugged in. So, I just bought my tube amp (peavy VT classic 212) and I need to know if/when I am gonna need to change the tubes and how to tell that they need to be changed.

 

[Lewguitar]

Re: how do i know when to change a tube

I really dont know anything about tubes/amps ect. except that if you f*ck with em you can fry the crap outta yourself even without it plugged in. So, I just bought my tube amp (peavy VT classic 212) and I need to know if/when I am gonna need to change the tubes and how to tell that they need to be changed.

I change 'em when I notice the amp not sounding as nice as it used to. Your ears will let you know.

 

[Skarekrough]

Re: how do i know when to change a tube

Look for to eb emitting fire....

Sure sign the tube's gone to the great gig in the sky.

 

[Kommerzbassist]

Re: how do i know when to change a tube

Uhm... AFAIK you can't kill yourself with an unplugged amp... at least not electrically

 

[Lewguitar]

Re: how do i know when to change a tube

Uhm... AFAIK you can't kill yourself with an unplugged amp... at least not electrically

The filter caps hold a charge even when the amp is unplugged and if you remove an output tube and do something like sticking a probe into the socket to try and tighten the pin holders of the tube socket you can get knocked on your butt...or so I've heard.

The filter caps need to be discharged before working inside the amp...even if the amp is unplugged

Lew

 

[marvar]

Re: how do i know when to change a tube

Uhm... AFAIK you can't kill yourself with an unplugged amp... at least not electrically

You'd better believe that you can kill yourself with the amp unplugged!
as Lew says, those filter caps hold a charge for quite a while-if you go mucking around inside your amp, you can get fried- and it's more voltage (dc)sometimes than the 120V that come out of the wall-
It's not so easy to take a hit while unplugging tubes, unless your hands are wet, or you are standing in a puddle of water- as long as you don't touch the pins of the tube while pulling it out of the socket- after you get them out-they are completely harmless,(the tubes that is) unless you break the glass. Then you might cut yourself!

 

[ErikH]

Re: how do i know when to change a tube

Uhm... AFAIK you can't kill yourself with an unplugged amp... at least not electrically

Oh yeah you can. Those big filter caps hold enough charge to kill you if you're not careful. They must be properly discharged when doing any heavy duty service inside the amp. Tube changes are one thing, but mucking with the sockets or any other part without discharging them is just asking for a jolt you really don't want.

 

[Kommerzbassist]

Re: how do i know when to change a tube

Are you sure those caps in an AMP deliver that much current? I mean yes, those things in CRTs can kill you left handed, but they're huge...
Could anyone of you guys try that thing with the caps out for me? (as I don't have a tube amp yet)

 

[ErikH]

Re: how do i know when to change a tube

Are you sure those caps in an AMP deliver that much current? I mean yes, those things in CRTs can kill you left handed, but they're huge...
Could anyone of you guys try that thing with the caps out for me? (as I don't have a tube amp yet)

Yes, they can. Even though the voltage going in to the amp is 110-120v AC, the input transformer increases that voltage to a much higher amount, over 300 volts in most tube amps. Those filter caps see that higher voltage. They are used to "filter" the power and keep it as clean as possible. Those types of caps can hold a heavy charge for months even when the amp is never used during that time. The amount of charge does trickle down over time but considering the amount they can hold, it takes a long time for them to naturally discharge to safe levels.

 

[Kommerzbassist]

Re: how do i know when to change a tube

Yes, they can. Even though the voltage going in to the amp is 110-120v AC, the input transformer increases that voltage to a much higher amount, over 300 volts in most tube amps. Those filter caps see that higher voltage. They are used to "filter" the power and keep it as clean as possible. Those types of caps can hold a heavy charge for months even when the amp is never used during that time. The amount of charge does trickle down over time but considering the amount they can hold, it takes a long time for them to naturally discharge to safe levels.

But shouldn't they be unloaded when there are still speakers attached?

 

[ErikH]

Re: how do i know when to change a tube

But shouldn't they be unloaded when there are still speakers attached?

No, not at all. The speakers have nothing to do with discharging the filter caps. The amp isn't being turned on while discharging the caps. That would defeat the whole purpose of discharging them just for them to charge up again.

 

[Lewguitar]

Re: how do i know when to change a tube

One way to discharge the filter caps is to turn the power switch to off but leave the standby switch "on". Then strum your guitar until you no longer hear any sound through the speakers. You don't need to discharge the filter caps when you change tubes though...just when you're going to be working inside the amp or retensioning the tubes sockets or something like that. Lew

 

[ErikH]

Re: how do i know when to change a tube

You're right Lew, you can do the power off, standby switch in the "on" position. But even after that, there's still some charge left in them. Not as much obviously but enough to tingle.

 

[Rocker35]

Re: how do i know when to change a tube

I'm a highly qualified electrical engineer and it's not the volts that kill, it's current. As little as 100mA is enough to kill!!!!

 

[motorboy29]

Re: how do i know when to change a tube

like i said, they'll kill you if you f*ck with 'em (just like commies:6, anyway, how do I know when to change the tubes (remember, ive never had a tube amp before) aside from any explosions of anything rediculous like that

 

[ErikH]

Re: how do i know when to change a tube

If it's brand new, you're fine. If you got it used and the previous owner is not sure when it was last retubed, then go ahead and retube it, pre-amp and power tubes. Then go from there. A retubing depends on how often the amp is used, how hard it's pushed, the elements it's used in, etc. Playing it at home in the garage once a week or so doesn't warrant frequent tube changes, probably every year or two, again depending on how hard those power tubes are pushed. Played loudly in a smokey bar 5-6 nights a week will warrant more frequent tube changes. And again, listen to how it sounds with fresh tubes. When it doesn't sound like that anymore, then it's most likey time for a change.

 

[DesertRose]

Re: how do i know when to change a tube

Usually there will be those red lights glowing in the tubes.
Think when they're outta action those red lights will not lid up I guess.
Prolly thats one way to tell that a tube is busted

 

[Chaos]

Re: how do i know when to change a tube

I'm a highly qualified electrical engineer and it's not the volts that kill, it's current. As little as 100mA is enough to kill!!!!

Correct. Current is what kills you, however 100ma would have little affect on contact with unbroken skin.

Most likely you'll injure yourself when your hand smacks something hard as you instinctively jerk it back after you accidentally short a cap.

 

[motorboy29]

Re: how do i know when to change a tube

Right, so i got it used and the tubes are kinda old-lookin and black on the bottom... I prolly need to change 'em. Please tell me its easy... like changing light bulbs or somethin. Also, what ones do I need and where do i get them and poss. instructions on how to do it.

 

[marvar]

Re: how do i know when to change a tube

My advice is to take it in to a electronics or amp tech- changing the tubes is no big deal-however-setting the bias takes some knowledge of the inner workings of an amp-at the same time, he will probably give a look at, and inform you of any things amiss- which could lead to problems in the future- go aead and eat the cost- but don't let them overcharge you for tubes! You can even buy your tubes somewhere else and let the tech install them for you.
at least your amp will get a clean bill of health, and you will be in good shape.