When good tubes go bad...

[FAC]

Hi Folks,

Do tubes fail gradually (like strings becoming dull over a period of time) or suddenly (like a light bulb burning out) or in some other fashion?

Are there common precursors to impending tube failure (besides smoke/flames)? I've heard of tapping them gently while the amp is on to assess the degree of microphonics. Any other tips?

Any insight would be greatly appreciated.:thanks:

 

[wahwah]

Re: When good tubes go bad...

Extraneous noises are generally a good indicator, crackling, whistling, humming...although those last two could just indicate that they don't know the lyrics...



Cheers..........................wahwah

 

[Boogie Bill]

Re: When good tubes go bad...

Hi Folks,

Do tubes fail gradually (like strings becoming dull over a period of time) or suddenly (like a light bulb burning out) or in some other fashion?

Are there common precursors to impending tube failure (besides smoke/flames)? I've heard of tapping them gently while the amp is on to assess the degree of microphonics. Any other tips?

Yes, tubes can fail dramatically. I had about an hour on a new EH12AX7 I'd received from thetubestore.com. I took my newly acquired Mesa Mark III 112 EVM combo to a local jam, and it shorted out in a most spectacularly psychedelic fashion on the second verse of "Black Magic Woman"...screeching and moaning like a banshee in heat! Half the audience thought it was a cool effect, while the other half was going, "WTF!!!" Quite embarrassing, though.

The Good News: thetubestore.com sent me a new EH12AX7 the next day, at no charge. That's really great service.

So, yes they can go bad instantly. They also deteriorate over time, like tires on a car. Tubes in a combo amp can be subject to tremendous vibration that can lead to microphonics. You'll often hear this as squealing; or it can give the amp a hard, brittle, edgy, or smeared tone.

I'm very conscious of using my STANDBY to let the tubes warm up before slamming them with a high voltage signal. And, I try to let my amp cool down before I GENTLY place it in my car. The filaments are fragile when hot.

If you check the Mesa Boogie site, they have PDF file Owner's Manuals for most of their amps. Usually at the back, they have several paragraphs on tube basics. It's a good resource.

Bill

 

[FAC]

Re: When good tubes go bad...

If you check the Mesa Boogie site, they have PDF file Owner's Manuals for most of their amps. Usually at the back, they have several paragraphs on tube basics. It's a good resource.

Bill

Thanks! I'll check that out.

 

[Lewguitar]

Re: When good tubes go bad...

When it comes to 12ax7 type preamp tubes, I find that I can use them for years and years...or until they become noisy/microphonic. I rarely wear them out...they become noisy and then I replace them.

Rectifier tubes can last a long long time too.

I rarely wear down power tubes either. Seems like I replace them when they suddenly go bad: start glowing red inside and humming. Soon as that happens I change 'em because they can fry the tube socket when they suddenly go sour.

So for me at least, tubes don't really gradually wear down and lose tone. They just fail!

Lew

 

[Gearjoneser]

Re: When good tubes go bad...

Feel the inside of the amp's cabinet and chassis after the amps been running awhile.
If it's blazing hot, enough to warp tolex, there's a high likelihood that it's biased too hot, and that'll wear out tubes faster than anything, not to mention cooking tube sockets or other nearby components.

 

[FAC]

Re: When good tubes go bad...

...So for me at least, tubes don't really gradually wear down and lose tone. They just fail!

Lew

It might sound funny, but this makes me feel better. As a natural born worry-wart, I started to wonder if the tubes might gradually sound crappier and crappier at a slow enough rate that I would not notice 'til the tone was just awful...Thanks for your input.

 

[muttonchopsrule]

Re: When good tubes go bad...

the answer to the original question: both.

sometimes they'll fail suddenly like Boogie Bill said. OTOH, usually a good tube will wear over time. it's one of those things that happens so gradually that one day you'll think to yourself "man, my amp just doesn't sound quite as good as it did this time last year... must be time for some new tubes".