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Post subject: bad tubes
Posted: Fri Sep 23, 2011 10:56 pm
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What are some signs that a power tube is bad or a preamp tube?


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Post subject: Re: bad tubes
Posted: Sat Sep 24, 2011 1:56 am
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Spurious/anomalous noise, sonic degradation, and reduced output are all reliable indicators that something is amiss.

And of course, smoke and/or fire emanating from an amp is never a good sign.

:lol:

Arjay

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Post subject: Re: bad tubes
Posted: Sat Sep 24, 2011 3:12 am
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+1 Retroverbial

Sometimes ie very hard to hear the tubes are bad; they could be only weak and this happened very slowly you can't hear the difference.

Like a "not new" strings on a guitar and when you put new one NOW you hear your old one are weak.

Most of the time the only tubes to check and replace are Phase Inverter , the tube close from the outputs tubes and the output tubes.

The other preamp tube normally last very long . Bur I should admit that modern tube could fail. New old stock have a very long life.


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Post subject: Re: bad tubes
Posted: Sat Sep 24, 2011 5:57 am
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Loss of volume of pops fuses


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Post subject: Re: bad tubes
Posted: Sat Sep 24, 2011 9:08 am
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weird sounds for an amp

watch out for
power amp tubes sounding like someone is mowing outside - low hum
preamp tubes like someone is cooking bacon - sizzling or cracking


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Post subject: Re: bad tubes
Posted: Sat Sep 24, 2011 12:54 pm
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On top of all, abnormal sparks in vaccum (sometime visible in the dark).

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Post subject: Re: bad tubes
Posted: Sat Sep 24, 2011 10:20 pm
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Thanks guys I was playing the other day had some overdrive going and the volume started to fade. Now when i play real easy its fine but as soon as i give her some gas the speaker sounds like a blown speaker. So I dont know if its tube or speaker.


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Post subject: Re: bad tubes
Posted: Sun Sep 25, 2011 2:34 am
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Try to connect your amp to another speaker. It's the easiest solution before replacing tubes


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Post subject: Re: bad tubes
Posted: Sun Sep 25, 2011 2:37 am
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stratele52 wrote:
Try to connect your amp to another speaker. It's the easiest solution before replacing tubes


+1

Isolating the issue is the first step to successful troubleshooting.

Arjay

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Post subject: Re: bad tubes
Posted: Sun Sep 25, 2011 10:29 pm
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that was my plan just have to find a speaker to test with. Thanks guys.


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Post subject: Re: bad tubes
Posted: Wed Sep 28, 2011 4:42 am
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My experience with power tubes, as they get old they start needing the bias to be tweaked "hotter" and "hotter" to get the same mV (really mA) idle reading. If power tube don't hold a steady a steady bias, but the value wanders all over the place (with no guitar plugged in and volume(s) at zero)---you may have bad tubes. Esp if you can substitute another set and the amp then can hold a steady bias.

It could just be one bad power tube. You'll need to rotate tubes and check the bias, to find the bad one.

As for input/gain stage/EFX/phase inverter tubes---they usually become noisy. Hissy, microphonic, sensitive to the most gentle touch = distinct noise from the speaker (at volume). Or like other said, they have a "dead strings" sound. That is apparent when you replace the dying tube with a fresh one.


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Post subject: Re: bad tubes
Posted: Wed Sep 28, 2011 5:00 am
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+1 BMW2002Ti

You understand and explain very well the use of biasing tubes as they get older


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Post subject: Re: bad tubes
Posted: Wed Sep 28, 2011 6:52 am
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stratele52 wrote:
+1 BMW2002Ti

You understand and explain very well the use of biasing tubes as they get older


+2!

Arjay

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Post subject: Re: bad tubes
Posted: Wed Sep 28, 2011 3:36 pm
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+3..........thousand. Coincidence? :o

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Post subject: Re: bad tubes
Posted: Thu Sep 29, 2011 4:34 pm
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It looks like it is a bad power tube. A new set of JJ on there way. thanks to all. As always i would like to hear any advice you have to give. Not only helps me learn but others as well. Any thing i should really know on putting in new tubes would be great.


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