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Post subject: 1979 Twin Breaks Early
Posted: Thu Feb 18, 2010 6:52 pm
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My 1979 Twin Reverb breaks at 2.5...should it? Does this mean I should replace the caps?


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Post subject: breaks?
Posted: Thu Feb 18, 2010 7:41 pm
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what exactly happen at the break... power off, only sound is being affected, a slap sound, it could be another thing than the caps. if you have more info please add so we can give you some help if we can or know something.

Ivan :idea:


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Post subject:
Posted: Fri Feb 19, 2010 4:00 am
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ntibert,

Do you mean your amp begin to overdrive at 2.5 ?
(It should not, not before 6-7)

If your answer is yes, It's because your output tubes needs to be bias or a replacement. One or more tubes


Questions :

Do you change somes parts or tubes or make a tune-up before this " breakup at 2.5 " ?
If you don't : bias and/or output tubes replacement.
If you do : Is it a good parts or tubes, exact replacement ? Good technician do this joB ?


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Post subject:
Posted: Fri Feb 19, 2010 4:43 am
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The tubes "overdrive" or saturate? at 2.5 which could be regarded as a positive thing for a Twin, but I'd rather have the clean headroom. Don't get me wrong, this is plenty loud for this 135 watt beastie. I simply find the breaking hard to control when playing outdoor venues. I installed a new set of JJ's last year and I did try out a set of Groove Tubes from my 65 Reissue Twin but I noticed little difference. Overall, this amp quite amazing with a real Keith Richards sound. I thought it might also be that the speakers are old.


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Posted: Fri Feb 19, 2010 6:49 am
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A Twin should be clean from 1 to 5-6.

You didn't tell if you make a bias ( or check it) when you put the new tubes ( JJ)

Maybe you just put new tubes in ! NEVER do that

You should ALWAYS make bias when you change tube.

This is why your amp break to early


Break too early = no good bias = tubes working very hard = tubes could fail = your amp did not give you the best tone


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Post subject:
Posted: Fri Feb 19, 2010 8:46 am
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I have not checked the bias.....better look into that. Thanks!


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Post subject:
Posted: Fri Feb 19, 2010 11:22 pm
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Hi Bert, this break-up is happening on both channels? Have you tried running the amp through the Reissue Twin's speakers? The '79 is a different output section than the Reissue. But before getting too excited about the amp, if you can switch the speakers between both amps,for a comparison, then that will eliminate one variable. You know what I mean, run the Reissue into the '79's speakers and the '79 into the Reissue's speakers. The speaker load should be set at 4ohms on the '79,for the test. I'm going to recheck your '79 schem, but it should be a 4ohm load for the stock speaker set-up. Art

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Post subject:
Posted: Fri Feb 19, 2010 11:35 pm
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Yeah, the '79 is 4ohm all the way, good to go for a test. I am computer challenged. So I lose this forum when I go to schem heaven. Art

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Posted: Sat Feb 20, 2010 11:04 am
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stratele52 wrote:
A Twin should be clean from 1 to 5-6.

You didn't tell if you make a bias ( or check it) when you put the new tubes ( JJ)

Maybe you just put new tubes in ! NEVER do that

You should ALWAYS make bias when you change tube.

This is why your amp break to early


Break too early = no good bias = tubes working very hard = tubes could fail = your amp did not give you the best tone


+1

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