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Post subject: First major tube failure of my drri
Posted: Mon May 02, 2016 8:41 pm
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Well, I guess it couldn't have happened at a better time.... If there's such a thing as a "better time". This happened right after rehearsal yesterday. I gave it a thorough look over, slapped in some new tubes and biased it up. It's back in action for hopefully another, mmmm, couple of years, at least.

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Post subject: Re: First major tube failure of my drri
Posted: Mon May 02, 2016 10:22 pm
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Tragic.

As they say in the Mexican army......

¡Mierda hace!

:(

Arjay

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Post subject: Re: First major tube failure of my drri
Posted: Tue May 03, 2016 6:40 am
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Interesting the old tube has a smoked glass cover to hide the fact that there is no carbon coating on the plate.
The carbon coated plate in the most important feature of a good tube.
While you're at it, I would rekit all the tubes for better performance.


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Post subject: Re: First major tube failure of my drri
Posted: Tue May 03, 2016 7:00 pm
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It would appear that the one in the foreground has possibly lost some, if not all, of its vacuum.


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Post subject: Re: First major tube failure of my drri
Posted: Tue May 03, 2016 9:41 pm
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Arjay,

It certainly does. Just glad I've had great instruction from you and others on this forum to guide me through my vacuum tube learning curve.

Timsaudio,

Not a bad idea, maybe a new phase inverter for sure. After setting the bias I decided to check all the dc test points on the schematic, they all were either pretty close or within a ten percent tolerance. Tim, I thought the smoked glass was used as a shielding to help reduce noise. But it's good to know about the carbon coating. Thanks for the info.

Evets618,

I concur. :D

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Post subject: Re: First major tube failure of my drri
Posted: Wed May 04, 2016 3:21 am
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Wait a minute....US made tubes failing? This has never happened before.....ever. All reports are that the US made tubes have never failed in the whole history of mankind. How can this be? :?

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Post subject: Re: First major tube failure of my drri
Posted: Wed May 04, 2016 6:35 am
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These are GE made tubes (188 manufacturer's code). March 1948 vintage. Usually, very tough tubes. Sorry to hear they went bad. You may want to tighten the 6V6GT tube sockets. Loose fit can sometimes lead to loss of bias voltage. Esp, in combo amps that have a lot of onboard vibes from the speaker.

BTW... the dark glass was part of some WW2 mil spec requirements, for their transceivers. Supposedly, to help with EMF interference.

Good luck with the new tubes! :)


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Post subject: Re: First major tube failure of my drri
Posted: Wed May 04, 2016 7:15 am
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evets618 wrote:
It would appear that the one in the foreground has possibly lost some, if not all, of its vacuum.

:wink:

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Post subject: Re: First major tube failure of my drri
Posted: Wed May 04, 2016 8:34 am
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Yes, I've spilled vacuum on my bench as well. It's very difficult to clean up.....


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Post subject: Re: First major tube failure of my drri
Posted: Wed May 04, 2016 9:53 am
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TimsAudio wrote:
Yes, I've spilled vacuum on my bench as well. It's very difficult to clean up.....


Almost as elusive as trying to recover that blue "magic" smoke that often escapes after a botched mod.

:mrgreen:

Arjay

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Post subject: Re: First major tube failure of my drri
Posted: Sat May 07, 2016 5:55 am
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What !
Those tubes only lasted 68 years !!!
Disgraceful :roll:

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Post subject: Re: First major tube failure of my drri
Posted: Sat May 07, 2016 12:55 pm
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shimmilou wrote:
Wait a minute....US made tubes failing? This has never happened before.....ever. All reports are that the US made tubes have never failed in the whole history of mankind. How can this be? :?


blues bondsman wrote:
What !
Those tubes only lasted 68 years !!!
Disgraceful :roll:


Oh the humanity.... :lol:

So went with a couple of EH 6v6's. On the hunt for a solid 12at7 for the phase inverter. I've read good reviews about the JAN Phillips 12at7wa, but i also havent been let down by any brand of 12at7 ive used on my other amps. Just goes to show, i guess.

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Post subject: Re: First major tube failure of my drri
Posted: Sat May 07, 2016 2:40 pm
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All in good fun my friend ! :mrgreen:

I bought a bunch of Magnavox 12AT7 a while back that have held up well in my Silverface Super reverb
At least two of them have !

The only catastrophic meltdown i've had with older USA tubes was a 5881 in a messed up 69 bassman head, that had yet to be doctored on, i've had JJ's EH and a few Ruby tubes go KABOOM ! or maybe just fizzle and die ???
Even my beloved Tung-sol reissue 6V6GT's caused some damage in one of my DRRI's

Besides Shimmilou knows I value his opinion 8)

A buddy dropped off his JCM-900
Lucky for him it detonated at the end of practice and not it the middle of a gig !
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