# Tube amp volume keeps dying?



## EchoWD40 (Mar 16, 2007)

Well i recently got a couple tubes replaced at a local place, but it didnt fix my initial problem. You see, i am having a problem with my amp where it keeps going to like zero volume (not completely of but barely able to hear) and then it picks up again at normal volume. Best way to describe it as a tremolo effect but it does it at random and it's really starting to piss me off. Any ideas on what could be the cause of this? Maybe my power amp is dying? 
Let me know if you guys have any ideas.


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## Ripper (Jul 1, 2006)

A bit more info is needed. What model and make of amp is it?


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## greco (Jul 15, 2007)

Did you take it into the local place to specifically repair the problem you are posting about? If yes, have you talked to them recently...... as it appears that they have not finished the repair job. 

Was the volume working OK when you picked up the amp from the local repair place?

I'm not sure that it will help, but you might want to post the make and model of your amp. and which tubes were replaced.

Something seems strange here ....??


Cheers

Dave

Ripper and I were posting at the same time...he won. Which is good because he is an electronics guru.


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## guitarman2 (Aug 25, 2006)

Have a look at this link.

http://www.geofex.com/ampdbug/lowpower.htm


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## EchoWD40 (Mar 16, 2007)

greco said:


> Did you take it into the local place to specifically repair the problem you are posting about? If yes, have you talked to them recently...... as it appears that they have not finished the repair job.
> 
> Was the volume working OK when you picked up the amp from the local repair place?
> 
> ...


The Amp is a KUSTOM 72 Coupe head. 
What i had it there for was to repair white noise at the top end (full volume) and he did that. 3 12ax7 tubes were replaced and i replaced all the 6l6's previously. 
The amp did this at random before, and i thought it might have been the bad tubes (12ax7's). When i got it back, it was fine, but again i must stress this is at complete random.


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## keeperofthegood (Apr 30, 2008)

I am, as I have said before, a LOT rusty on amps and their repair; however, as I recall, capacitors can have two obvious fail modes. Either they go open, or short. While entering either of these modes their behaviour can drift. Motor boating is a good one for beginning to short, and 60hz hum for going open. That's the obvious one.

I say two obvious because there are others, and I have encountered different fails that "look" capacitor related but aren't quite. Capacitors usually have a resistive path that transfers their charge, or there are two capacitors and signal is take from between them. When the resistive path fails either the charge does not get applied to the capacitor (acts open) or the capacitor fails to discharge and acts as a barrier to signal (or the second capacitor shorts and ties the other capacitor high also then acting as a barrier).

My intuition would be to look for over heating resistors; that would be my suggestion (or best guess) to why you have seemingly normal operation for a period, then a ramping to silence  A visual inspection should be easy enough, and over heating parts are sometimes visually apparent though not always.

Too bad it is a Kustom, I do not know where to get their schematics :/ maybe one of the others will.


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## greco (Jul 15, 2007)

TDeneka said:


> The amp did this at random before, and i thought it might have been the bad tubes (12ax7's). When i got it back, it was fine, but again i must stress this is at complete random.


Thanks...now I understand how random this really is. 

I'm looking forward to hearing what everyone has to say regarding the possible cause/solution of this problem.

Consider this a bump from an electronics enthusiast (AKA beginner)

Dave


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## Wild Bill (May 3, 2006)

TDeneka said:


> Well i recently got a couple tubes replaced at a local place, but it didnt fix my initial problem. You see, i am having a problem with my amp where it keeps going to like zero volume (not completely of but barely able to hear) and then it picks up again at normal volume. Best way to describe it as a tremolo effect but it does it at random and it's really starting to piss me off. Any ideas on what could be the cause of this? Maybe my power amp is dying?
> Let me know if you guys have any ideas.



It could be a zillion and one things! Resistors could be opening up (not just to overheating - they might be cool as a cucumber and look fine on the outside) or a coupling capacitor might be failing. A control could be dirty. A tube can have intermittent faults.

I could write a book! This is not a simple sort of thing that someone can just give you a quick tip. The amp needs a good tech. If it were in my shop I would open it up on my bench and plug a signal generator into it so I could hear it run while I worked on other stuff. Eventually the amp would start to act up and I could run over and start checking with a meter or 'scope probe. The reason for this tactic is that when the amp is working fine there's usually nothing bad to measure!

By process of elimination eventually the fault is revealed.

Somebody might have a good tip that an amateur can use. You might win the lottery too!:smile:

If I were you I would just take it to a good tech. Is there a warranty on the amp?

:food-smiley-004:


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## EchoWD40 (Mar 16, 2007)

Wild Bill said:


> It could be a zillion and one things! Resistors could be opening up (not just to overheating - they might be cool as a cucumber and look fine on the outside) or a coupling capacitor might be failing. A control could be dirty. A tube can have intermittent faults.
> 
> I could write a book! This is not a simple sort of thing that someone can just give you a quick tip. The amp needs a good tech. If it were in my shop I would open it up on my bench and plug a signal generator into it so I could hear it run while I worked on other stuff. Eventually the amp would start to act up and I could run over and start checking with a meter or 'scope probe. The reason for this tactic is that when the amp is working fine there's usually nothing bad to measure!
> 
> ...


Amp is pretty old as it is now. and i am not sure of any good techs, but ill give mike fortin a call, and see if he can help out. Thanks guys!


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## Lemmy Hangslong (May 11, 2006)

could be something as simple as a loose connection... especially where stacon terminals are used this is a viable possible reason for your amp cutting in and out randomly.

Craig


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## hackman (Jan 2, 2012)

My 72 coupe combo was loosing volume the same way...took back panel off and the 10w390ohm resistor had broken loose...this is for the standby circuit...replaced with a 330 ohm and is running too hot so I ordered the correct resistor...hope this helps anyone


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