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GMC Forum _ GEAR & PRODUCTION _ Problem With Powertubes

Posted by: Constie Nov 15 2007, 02:29 AM

Hi there

I have a problem with my all-tube amplifier. Maybe you know what's the problem, if not I'll visit the technician.

So the first powertube is just glowing a little.
But every second one is glaring like a glow-lamp.

Which is right?


I noticed that as I was changing preamptubes to fix a problem.

Do you know what to do?

Posted by: MickeM Nov 15 2007, 02:43 AM

QUOTE (Constie @ Nov 15 2007, 02:29 AM) *
Hi there

I have a problem with my all-tube amplifier. Maybe you know what's the problem, if not I'll visit the technician.

So the first powertube is just glowing a little.
But every second one is glaring like a glow-lamp.

Which is right?
I noticed that as I was changing preamptubes to fix a problem.

Do you know what to do?

Uneven bias maybe?

Posted by: Constie Nov 15 2007, 02:59 AM

QUOTE (MickeM @ Nov 15 2007, 02:43 AM) *
Uneven bias maybe?

Maybe.
The funny thing is: I bought it at ebay.com and a friend of mine shipped it to Germany.
The description said it's almost new. Yes, optically there are no scratches or something else but one footswicht button doesn't work right. Okay that's no problem.

Then I noticed that the clean channel wasn't very load at all. I pulled everything up and could play in my little room. So I decided to change some tubes: I replaced the preamp tube for clean-channel with one for the distortion. That didn't fix the problem.
whatever...

Then I saw the powertubes. I'm really sad, because I think I got cheated. Nothing works well and I payed a lot of money for it sad.gif

Posted by: tonymiro Nov 15 2007, 03:05 AM

I think MickeM is right here about the bias. I'd take it to an amp tech and get them to give the power amp a check over. Might need something like a re-bias or new power tubes.

Cheers,
Tony

Posted by: Muris Nov 15 2007, 03:07 AM

Yeah,bias or replacing the tubes.

Posted by: Constie Nov 15 2007, 03:11 AM

Alright, thank you guys.
I was trying to avoid that because 65 pounds (30kg) are a lot to carry.
Especially if the next technician is about 1hour travel time away.

Posted by: Muris Nov 15 2007, 03:14 AM

Can someone give you tubes to try them,a friend or som?
That's pretty heavy to carry around... huh.gif

Posted by: Constie Nov 15 2007, 03:22 AM

QUOTE (Muris @ Nov 15 2007, 03:14 AM) *
Can someone give you tubes to try them,a friend or som?
That's pretty heavy to carry around... huh.gif

Hey good idea. But I'd need six powertubes.
Anyway I'm gonna ask my guitarteacher, maybe he has.

By the way: Could this problem be caused by the cabinet? A mismatch or something like that?
Because I bought it very cheep and it's quite old.

Posted by: Muris Nov 15 2007, 03:26 AM

Mismatch in Ohms between amp and cabinet might cause lacking in amp's work/power,
but I doubt It has something to do with glowing of tubes...
Tony,Andrew,MickeM?

Posted by: MickeM Nov 15 2007, 03:40 AM

QUOTE (Muris @ Nov 15 2007, 03:26 AM) *
Mismatch in Ohms between amp and cabinet might cause lacking in amp's work/power,
but I doubt It has something to do with glowing of tubes...
Tony,Andrew,MickeM?

What rhyme did Andrew teach me before? bla bla bla dn your head will fry. lol, I will look it up. "Speak too high and your head will fry", i remembered, thanks Andrew lol

Which should mean that if the speaker Ohm is too high the head may get damaged. (Right, master?) No glowing tubes though, I don't think so. ???

Posted by: Muris Nov 15 2007, 03:53 AM

laugh.gif Great rhyme

Posted by: tonymiro Nov 15 2007, 05:45 AM

Yes if the speaker load is incorrect then you will have problems. Too high and presumably the second output coil of the transformer can overload and might fry the power tubes. But I think the load your talking about to do that is significant. I don't see why it would be some rather then all the tubes that are acting up that sounds more to me like a balance problem. I'd take it off to a tech to be sure. Andrew would know more though then me.

Cheers,
Tony

Posted by: Pavel Nov 15 2007, 05:56 AM

QUOTE (Muris @ Nov 15 2007, 03:53 AM) *
laugh.gif Great rhyme


We will soon all start talking in rhymes, we're all members of musician's community after all! laugh.gif laugh.gif

Posted by: Muris Nov 15 2007, 06:08 AM

Where's Andrew btw??? huh.gif


EDIT
Oh yeah,told me about moving to his own house,congrats tho Andrew!!! smile.gif

Posted by: Andrew Cockburn Nov 15 2007, 10:28 AM

QUOTE (Muris @ Nov 15 2007, 12:08 AM) *
Where's Andrew btw??? huh.gif
EDIT
Oh yeah,told me about moving to his own house,congrats tho Andrew!!! smile.gif


I'm here - was travelling on business today! House move is tomoorw and Saturday smile.gif

Anyway, MickeM remembered the rhyme right!

If the glow is coming from anywhere but the heaters that is very bad and could be down to bias problems. However, if they are different tube types between pre and power they may well glow different amounts. Bottom line sadly is take it to a tech to be sure ...

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