New to tubes. Need help determining if tubes are bad or not.

[willg95]

I have two tubes that I think have overheated and melted at the tips. But I'm really not sure. I'm fairly new to tube amps. When I play for a while at a medium volume it starts to get quiet and I can smell the heat from the amp. I removed the tubes (with a cloth of course. I do know a little about handling them ) and took a picture of the tips. Can anyone confirm they overheated or has something else happened?



They are 6L6GC tubes and I will admit, they are from a regular guitar amp. And they're out of a Peavey Vypyr 60W combo. Please no hate on guitars, folks. I just didn't feel like finding a specific guitar forum just for this issue. Help is GREATLY appreciated.

[almightycrunch]

Ok, first, they are not halogen light bulbs, skin oils wont "burn" them out.
second, nothing is melted at the tip, that is how they are made
third, you can pretty much always smell heat from a tube amp.
fourth, volume fluctuations would suggest that you need a new pair of 6l6's likely.

[BogeyBass]

If those are the original tubes or if you had them for more than 2years i would change em.

But the silver stain you see at the top of the tube is called the "Getter" its a silver coating applied to the tube in manufacturing.

Even after the tube is pumped out with a vacuum during manufacturing. There can be other gases considered contaminates inside. Over the life of the tube the getter will absorb contaminates which is a chemical reaction stimulated by heat from the tubes heaters.

So when you hear about guys "burning in" new tubes. People will often leave new tubes running for 24 hours. Then often claim a improvement in sound after burning in. Basically you giving the tube getter more of a chance to absorb contaminates from manufacturing, before pumping alot of power into a new tube. Most quality tubes have usually been tested and burned

just grap a pair of some new JJ's and be done with it....

[4StringShooter]

Originally Posted by BogeyBass;11218805[/URL

and be done with it....

<< So when you hear about guys "burning in" new tubes. People will often leave new tubes running for 24 hours.>>

You mean in Stand-By Mode???

NOT in " go " mode.

[BogeyBass]

Originally Posted by 4StringShooter

You mean in Stand-By Mode???

NOT in " go " mode.

As long as the heaters are on the getter will be doing its job.

At some point you would want to apply plate power and run signal threw it. leaving an amp in standby for extended periods of time is generally not recommended.

anyhoo the whole burn in thing is a little off topic..and is somewhat a audio snake oil or myth. so i was kinda just stirring things up...darn you caught me....

[nashvillebill]

You can handle tubes with your fingers all day long without fear. I've seen ancient tubes that were covered with some pretty gross crud, and they were still chugging along happily.

What amp is this, how old? If it's an older amp, it wouldn't hurt to have a qualified tech check it over. (the difficulty is finding a qualified tech, there's tons of folks that claim to be techs but they couldn't count their fingers and get the same number twice)

If you are going to replace power tubes, it would be a good idea to replace all of the power tubes (the big 6L6GC's). Most folks get them matched when they order them. Sovteks or JJ's are fine.

edit: I'm not a believer in the "gotta burn them in" theory. Just plug them in and start playing IMHO, just keep an eye on them at first to make sure they aren't glowing really bright cherry red...that indicates issues.

[B-string]

BTW there is no difference between tubes for bass use and guitar use, new tubes should have the bias checked by a qualified tube amp tech. If those tubes are used transplants the bias may be wrong in that amp for those tubes.

[willg95]

Alright, thanks for the replies!

I'm probably just going to get a new set. But in light of some comments, I'm not sure if they're even bad or not. But then again, nothing would explain the drops in volume. I also didn't know I could handle them safely without a cloth. That's what I get for listening to a guitard

I plugged them back in and played on the amp for a while. It seems to work fine. They glow orange in the middle. But when I take it off of standby, the glass illuminate a violet blue color. Is that normal? From what I just looked up, it seems to be normal.

[Caca de Kick]

Yes when you take it off standby, the tubes will glow with a blue-ish hue. Normal.

[Mr. Foxen]

If the grey metal part (the bit with holes in) itself is glowing, then that is red plating, and is bad, there should be a glow from inside, but the bulk of the metal inside should not glow. Might be your problem, biased too hot. Valves change their bias point over their life, so often a rebias rather than replacing is what is needed after a couple of years, as they wear in.

[johnk_10]

if they're two years old, it doesn't matter how old the tubes are, it matters how many playing hours on are on them. as long as they're pulling the correct current and meet the transconductance spec, they can last many many years. (500-1000 hours of playing time at the minimum.)

[staindbass]

2 years ? you must be a tube dealer lol. i have tubes from the 1940-50's that measure new and were used. since they are inexpensive it couldent hurt substituting a pair to see if it fixes the volume drop. about the volume drop, are you sure the speaker is the right impedance for the amp?

[okabass]

Looking the pic it seems that they have been too warm. The getter mirror has some grey edge. The edge should be like this.
http://www.tube-classics.de/TC/Tubes...M8-Tube-02.jpg
The tubes haven't probably damaged but too much warm is no good. Bias may be set too hot or you played too loud?

[BassmanPaul]

Originally Posted by willg95

But then again, nothing would explain the drops in volume.

There are many reasons for an amp to drop in volume. You should take the amp to a tech and not waste time by throwing money at it in the hopes that you fix the problem yourself.

[teleharmonium]

Originally Posted by staindbass

2 years ? you must be a tube dealer lol. i have tubes from the 1940-50's that measure new and were used.

Me too, but that's apples and oranges relative to new tubes. Current production tubes are not made nearly as well as the old ones, a couple of years is typical for current production power tubes in an amp used regularly.

[teleharmonium]

Originally Posted by willg95

I plugged them back in and played on the amp for a while. It seems to work fine. They glow orange in the middle. But when I take it off of standby, the glass illuminate a violet blue color. Is that normal? From what I just looked up, it seems to be normal.

A certain amount of blue glow is normal. If there's a lot of it, it means the vacuum is soft and the tubes need to be replaced. This is the sort of thing that is obvious if you see tubes side by side with and without this problem but hard to quantify for someone else using words. Tube testers will show that problem if it exists.

[teleharmonium]

Originally Posted by 4StringShooter

<< So when you hear about guys "burning in" new tubes. People will often leave new tubes running for 24 hours.>>

You mean in Stand-By Mode???

NOT in " go " mode.

No, burn in is done at full plate current. All standby mode does is run current through the heater, it's not going to burn in the tube. Traditionally, some burn in was done at the plant and then the tubes were tested, in some cases matched into groups, and then packaged.

[korngold]

Don't have time to read every post, but if you replace the POWER tubes, make sure you:

1) Get a matched pair of tubes (or a matched quad if your amp uses 4 power tubes)
2) Have a tech BIAS your amp.

Do not plop new power tubes in and assume everything is okay. You can burn out tubes or more important components if you don't have the amp biased after replacing power tubes.

[korngold]

Originally Posted by staindbass

2 years ? you must be a tube dealer lol. i have tubes from the 1940-50's that measure new and were used. since they are inexpensive it couldent hurt substituting a pair to see if it fixes the volume drop. about the volume drop, are you sure the speaker is the right impedance for the amp?

I'm with Staind--if the amp has seen minimal use, two years for tube replacement is excessive. My mesa combo has had the same tubes in it since about 10 years ago. But, I don't play it very often.

Also, an addendum to my previous post: some amps do not require biasing when you replace the power tubes (cathode-based amps). But, I think most 6L6 amps require biasing.

[IvanMike]

LOL - Talk about an inflammatory thread title!

I checked in to see if I needed to close a "tubes vs solid state" flame war....