Guitar amp. Tube overheating.


  #1  
Old 08-22-04, 01:36 AM
Terahertz
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Angry Guitar amp. Tube overheating.

Im borrowing an old guitar amp from my uncle. it runs on tubes and its a verry nice set. but when i turn it on it'l power up normaly and it'l work for about 30sec and then one of the tubes starts to heat up red hot, the whole thing glows even the plates and grid. also it doesnt start heating up like that unless it gets fed an audio tone, so unless i strum my guitar the amp wont act up. whats wrong with it. i hope its not the tubes because they are the discontinued 8417's, extreamly hard to find and if found are rare and very expensive. what do you think?
 
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Old 08-22-04, 05:49 AM
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Terahertz,

What make and model is the amp?

Did you ask your uncle if this is normal?
 
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Old 08-22-04, 10:22 AM
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Don't put any glue on it.
 
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Old 08-22-04, 06:13 PM
Terahertz
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The Make is: sgSystem
The Model is: sg-212

No that's not normal for the tube to over heat
 
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Old 08-22-04, 09:28 PM
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It looks like one of those times when it doesn't pay to borrow things.

I can't offer a solution but would suggest a shop look at it.
 
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Old 08-23-04, 07:46 AM
lumpy
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What of guitar are you using? More specifically, what type of pick-ups are on the guitar?
 
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Old 08-23-04, 12:40 PM
Terahertz
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Originally Posted by lumpy
What of guitar are you using? More specifically, what type of pick-ups are on the guitar?
its just a cheap profile, and i dont know what type of pickups they are. they are not pre amped though if that helps any
 
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Old 08-24-04, 08:41 AM
lumpy
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If you tap the jack before you plug it into the guitar does the tube have the same affect, ie heating up,or is it only when you actually strum the guitar. Also, how old is your cord?
 
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Old 08-24-04, 01:56 PM
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Try switching the tube with one of the other 8417s.
If the original tube you are having problems with starts
glowing red while in a different socket then the tube itself
could be bad. But if the other tube now starts glowing red
then the tube is not getting bias voltage from the chassis.
A common problem is the connection between the pins
of the tube and the socket. The first thing to check is
the socket itself. The metal contacts may need to be
pushed closer together to get a tighter fit. You can use
a tiny jewlers screwdriver for this. If connections are all
tight then they may need cleaned with contact cleaner.
"don't use Radio Shack" use Caig DeOxit you can get it
here.
http://www.partsexpress.com/pe/showd...number=341-200
This works great for cleaning other types plugs and connectors also.

If the connections are tight and clean and the problem still
persists then you probably have a passive component somewhere
in the chassis causing the trouble. "Possibly a resistor or capacitor"
You would have to send it to a shop to correct this.

If you plan to attempt any of this yourself just be warned that
voltages can run high in these amps. Carelessness can lead to a
shortened lifespan. If you have reservations then don't mess with it.

Hope some of this helps
Good luck
 
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Old 08-24-04, 08:29 PM
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Bias resistor to grid control circuit probably open or shorted.
If this is a push pull amp will have identical resistors on other 8417"s
Check the value of the resistors on the tube that works against the value of resistors on the one that is glowing hot.
 
  #11  
Old 09-06-04, 11:17 AM
Projo man
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Bias resistors

Sounds like you have some bias resistors that have gone south. Check under your output tubes 8417 you might find a resistor or 2 that have gone low in resistance. 100 or lower ohms, should be around 15K ohms give or take a few K. Here is a link to help you with the tube pin out. http://tdsl.duncanamps.com/show.php?des=8417
good Luck.
 
 

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