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Post subject: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 8:11 am
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Was at a band rehearsal and we were playing quite loud and the amp got dead quiet. It doesnt even hum. I've put my ear against the speaker at full blast, still no sound.

I have tried almost everything. I cant make it to do any sound, at all.

I think it might be the volume pot that might need a changing. It sounds almost like drops of water when i turn it. (There's no water in it. Heh.) I have also changed the tubes and checked all the tube-sockets and solder connections on the sockets.

Im lost here. Any help is greatly appreciated.

Btw, the slight blue light that comes from the output tubes when the amp is off-standby is not there. (It was before.)

What could be the problem?

Cheers
FF


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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 8:25 am
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Catastrophic failure...see Arjay's (Retroverbials signature) :? What kind of amp is it?

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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 8:48 am
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ddeaton107 wrote:
Catastrophic failure...see Arjay's (Retroverbials signature)


Can't be. There wasn't any smoke or fire.

:lol:

Providing some basic info about the amp would be useful......brand, model, age, etc.

My initial thoughts are that it's lost a critical voltage somewhere. As such, I'd start by investigating the power supply.

Arjay

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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 9:27 am
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The amp's a old Fender 75.

Been working (loud) for about 2 years now.

It's probably 40+ years old.


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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 9:46 am
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You say you don't see anything working is the jewel on?


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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 9:52 am
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The pilot lamp is glowing!
It's flickering just a wee bit sometimes, but i dont think that is the problem.

To answer your question; Yes, it is on.


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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 10:14 am
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Feelyfeels wrote:
Was at a band rehearsal and we were playing quite loud and the amp got dead quiet. It doesnt even hum. I've put my ear against the speaker at full blast, still no sound.

I have tried almost everything. I cant make it to do any sound, at all.

I think it might be the volume pot that might need a changing. sure it is not the volume Pot It sounds almost like drops of water when i turn it. (There's no water in it. Heh.) I have also changed the tubes and checked all the tube-sockets and solder connections on the sockets.

Im lost here. Any help is greatly appreciated.

Btw, the slight blue light that comes from the output tubes when the amp is off-standby is not there. (It was before.)

What could be the problem? Any fuse inside the amp ? Problem is in power supply section . No sound from the amp is one of the easiest problem for a qualified tech. Sometimes a resitors open , rectifier , in worst case Power Transformer . Do you have the right size of fuse ?

Cheers
FF


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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 10:18 am
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Shematic here ;


http://www.stratopastor.org.uk/strato/a ... _schem.pdf


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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 10:27 am
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There are 3 on the back and one inside!
None of them are blown!


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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 10:46 am
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Check to see if all tubes are glowing. If so... then you either need to check them with a tube tester or start subbing in new 12AT7, 12AX7, and 6L6GC one-by-one --- to rule out a bad tube.

Do you have a DVM? And a bit of circuit knowledge? If not, maybe tech time.


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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 10:47 am
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Feelyfeels wrote:
There are 3 on the back and one inside!
None of them are blown!



How do check them ? By eyes ? With meter ?


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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 10:50 am
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Tubes are fine..

I just looked at them to see if they had blown. I havent tested them.

I have a DMM, and basic circuit knowledge.


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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 10:58 am
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Feelyfeels wrote:
Tubes are fine..

I just looked at them to see if they had blown. I havent tested them.

How can you see they are not blow ? Are you kiding ?

I have a DMM, and basic circuit knowledge.


You check fuse with you meter ? Ohms scale with no power on OR AC volt scale with power ?


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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 11:28 am
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They are not visually blown.
Didnt even know that you could test them. Will try that soon.


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Post subject: Re: Amp suddenly got quiet.
Posted: Tue Mar 25, 2014 11:55 am
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Feelyfeels wrote:
They are not visually blown.
Didnt even know that you could test them. Will try that soon.


:lol: :lol: If tube in not broken in pieces you can't tell it is good or not .

Most Tubes tester ( if you talk about that ) can't test tubes amps. Tube tester drive tube at "idlle", not in working state . Like a car , if engine idle at park , are you sure you can drive the car at 60 miles per hour on highway ?


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