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Old 01-21-2013, 01:20 PM   #1
cGoEcYk
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Tube Amp Fades Out After 10 Sec

I found this ad... seems like a bargain. He says he's changed out the tubes but that the amp basically fades out/dies after being on for 10 seconds. Transformer issue? I love Marshall cleans... don't wannt pull the trigger without more info though.

http://albuquerque.craigslist.org/msg/3561040509.html
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Old 01-21-2013, 01:28 PM   #2
Robbgnarly
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It could be a variety of things honestly, but for $90 I'd get it. Your lucky I live in FL or I'd totaly ninja you
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Old 01-21-2013, 01:29 PM   #3
cGoEcYk
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I know I took my chances since probably no one else lives out here in the desert.

I read up a little more and it seems like this amp was designed such that it's prone to overheating, board could be melted. I found someone with a similar problem with the volume and they had it diagnosed by a tech as the OT being fried. Kinda on the fence about it.

Is the Celestion Heritage in it a good speaker?
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Old 01-21-2013, 01:32 PM   #4
gerraguitar
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if it's a good sounding amp then the fact that you're spending so little on it means you can spend the money to get it looked at by someone and fix it up. trust me you'll be glad you did if it's a promising amp
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I would recommend the marshal MG100

Very versatile and quality sound. It should treat you well
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Old 01-21-2013, 01:39 PM   #5
Robbgnarly
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Quote:
Originally Posted by cGoEcYk
I know I took my chances since probably no one else lives out here in the desert.

I read up a little more and it seems like this amp was designed such that it's prone to overheating, board could be melted. I found someone with a similar problem with the volume and they had it diagnosed by a tech as the OT being fried. Kinda on the fence about it.

Is the Celestion Heritage in it a good speaker?

The speaker alone you can get $90 for used so you can always sell it off if the amp is to expensive to fix. and you made your money back just by selling 1 part of the amp.
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2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
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GFS Greenie/Digitech Bad Monkey
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Old 01-21-2013, 01:55 PM   #6
Cathbard
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A dead OT won't fade out after 10 secs. That's just not the way they fail.
This sounds like an overheating component; possibly a rectifier, maybe a capacitor. My bet would be the rectifier (if it's solid state). Chances are that once you open it up you will see what has been overheating.
How you'd diagnose it would be a can of freeze if a visual inspection doesn't reveal anything. You gotta be mighty careful with freeze on a tube amp though, not a job for a beginner.


Edit: They do indeed have a solid state rectifier. I'd bet dollars to peanuts that this is suffering from the same design flaw as the early DSL's. ie an underrated rectifier. If that is the case then the solution would be the same - a bigger rectifier bridge that will take a heatsink - and a heatsink of course.
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Old 01-21-2013, 03:21 PM   #7
fly135
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I'd be all over that in a heartbeat. In addition to what Cathbard said, cracked solder joints change conductivity as the amp heats and causes symptoms like that. 10 secs is a little fast, but I'd definitely consider it as a possible cause as I have seen so many amps that have that issue.

I just picked up a Hot Rod Deluxe for $120 that emits a loud squeal after playing for a minute or so.

Edit: just did a quick search first post I looked at mentioned failing rectifiers.
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