changing my tubes!!! help!!!

[cris9288]

ok, so one of the power tubes in my amp shorted out. it's an el 34 from electro harmonix.

but before i go about replacing the set i have some questions:

typically, why do tubes short out? it would be good to know that way if i replace the bad tube, the new one doesn't short out immediately cuz there's another problem that's causing the tubes to short out.

can i just replace the one tube with the same one from the same company? can i replace it with a groove tubes one?

if i have to replace all four of them and i replace them with some groove tubes el-34's do i have to have the amp rebiased?

and finally, i was looking online for tubes, and they come in different groups: soft/hard/medium. wats the difference? any help would be great thanks!!!

[Enzo]

Tubes fail like light bulbs - tiny wires break free inside and touch something else. This coul dbe a manufacturing defect, or more likely just trauma from shipping.

[TubeDude]

Reason Why Tubes Blow

More than likely a resistor in the Output tube circuitry. That's the most common cause other than the bias just being way off. Check all the values of resistors in the output tube circuit to see if they are in spec. and change ones that aren't.

[bbartilson]

More than likely a resistor in the Output tube circuitry. That's the most common cause other than the bias just being way off. Check all the values of resistors in the output tube circuit to see if they are in spec. and change ones that aren't.

Can you explain this in more detail? I mean, the part where a resistor in the output tube circuit causes an output tube to fail?

In my experience, far more output tube failures have caused burnt resistors than the other way around. The most common cause of output tube failure I am aware of is physical shock, followed closely by wearing out from age. While certainly not as robust as they used to be, output tubes are overall quite robust and resilient devices in general. The typical guitar amp will survive a trip in the back of a truck for much longer than say, your laptop.

Best,
Bill

[Enzo]

ANd I don't get nearly the sustain from a laptop...


I would agree that it is far more likely a failed tibe will burn out a screen resistor than the other way around. Screen resistor opens or goes real high, all it does is shut down the tube

[bbartilson]

ANd I don't get nearly the sustain from a laptop...


I would agree that it is far more likely a failed tube will burn out a screen resistor than the other way around. Screen resistor opens or goes real high, all it does is shut down the tube

Careful there 'Zo. Digidesign has a new plugin called...you guessed it...Eleven.

I do not joke. Monster sustain from a laptop, no less.

But when the screen opens, the biggest problem I recall is that the flies get in. At least I have a vague recollection of something like that. Right now whether the screen is open or closed, all that comes in is snow.

[TubeDude]

What kind of amp are we talking about? Is it all stock including the speaker(s)? There's a lot of things that will cause the output tubes to short out. I've been working on tube amps for 20 years or so. I've seen some crazy stuff. Usually it's something simple or stupid that's causing it; such as mismatching the impedance of the speaker, etc. Also things as simple as not letting the tubes cool off before moving the amp. Also using "power attenuators" and things of that sort to get distortion at low levels puts a strain on things a lot more. Give some DETAILS about how this happened and exactly the model, etc... As I said before, the most likely cause is the plate or cathode resistor. Especially after the first tube blew. This usually messes up a plate or cathode resistor and throws the bias off. By the way, Electro Harmonix output tubes that I've seen are okay and sound decent but aren't that reliable in the long run. There are some exceptions to this though.

[cris9288]

i think it's interesting you guys are replying in this thread, it's been a while since i made that post. in case you all are wondering, the solution was simple. I was running my amp straight into the wall (no power strip). the voltage from a power outlet is very high, and without a surge protector of any kind the voltage was overloading my amp thus blowing a tube, and then the fuse. so i got a new set put it in, ran it through the same outlet with a power strip and well there you go. it's been a while now and i haven't had any tube problems.

[stokes]

i think it's interesting you guys are replying in this thread, it's been a while since i made that post. in case you all are wondering, the solution was simple. I was running my amp straight into the wall (no power strip). the voltage from a power outlet is very high, and without a surge protector of any kind the voltage was overloading my amp thus blowing a tube, and then the fuse. so i got a new set put it in, ran it through the same outlet with a power strip and well there you go. it's been a while now and i haven't had any tube problems.

In 40 years I have never used a surge protector,or power strip as you call it, with any tube amp,ever.I know there is a possibility that there could be a surge,but it never happened to me.The voltage from a power outlet is not "very high",unless there is a problem with your outlet,or a momentary surge.A "power strip doesnt lower you wall voltage,it just trips a breaker if there is a surge.You more likely just had a bad tube,and replacing them cured the problem,not the power strip.

[cris9288]

well, lets see. i replaced the tubes and plugged my amp into the same outlet without using a power strip and within thirty seconds one of the tubes blew, resulting in a blown fuse. just like before. so, since not all of the tubes from the last set were bad, i took a good one and replaced the new one that was no good anymore. i then hooked up a power strip and turned it on and it worked for hours (still works) without blowing the tubes. so there you have it.

[Rick Erickson]

Ah yes - once again: Correlation does impute causality....

[cris9288]

uh...wat do you mean by that?

[Alex R]

He means that no power strip and a new tube blowing might have happened at the same time, but aren't necessarily cause and effect. Now and then new tubes blow as soon as you fit them for reasons given earlier that are unconnected to power strips.

On the other hand maybe TubeDude is right and it's those pesky output tube plate resistors...

[cris9288]

well both of the situations in which the tubes blew were almost the same. In both cases a brand new set of tubes were present. in both cases, the tubes had all been working properly in another room and in the same outlet (with a power strip). And in both situations, the amp was taken into a different room and plugged into a different outlet w/out a surge protector. and in both situations the same tube (fourth one on the right) blew out after no more than thirty seconds of play. i instantly replaced the blown tube with a good one, plugged in a power strip and into the same outlet, and resumed play. but w/e, it doesn't really matter anymore, my amp has been working fine for a while now.

[TD_Madden]

Glad it's working out for you....

Out of curiosity, just what is the wall voltage?