Path: utzoo!attcan!telly!lethe!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!samsung!uunet!news.larc.nasa.gov!grissom.larc.nasa.gov!kludge
From: kludge@grissom.larc.nasa.gov ( Scott Dorsey)
Newsgroups: sci.electronics
Subject: Re: Tube Amp Output Trans. Bad ?
Keywords: Tube Amp Transformer Repair
Message-ID: <1991Feb25.151953.4299@news.larc.nasa.gov>
Date: 25 Feb 91 15:19:53 GMT
References: <1991Feb23.045313.29888@supernet.dallas.haus.com>
Sender: news@news.larc.nasa.gov (USENET Network News)
Reply-To: kludge@grissom.larc.nasa.gov ( Scott Dorsey)
Organization: NASA Langley Research Center
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In article <1991Feb23.045313.29888@supernet.dallas.haus.com> ktaylor@supernet.dallas.haus.com (Kurt Taylor) writes:
>I have replaced all the defective parts that I can find. Even replaced
>all of the tubes with known good ones. All voltages are correct. Still 
>there is a loud screech at the speakers when the amp is powered up. Could
>this mean that the output transformer is bad ? How can I test it ? Is there
>something else that I am overlooking ?

   If there is a loud screech at the output, then there is something which
is going into oscillation.  Disconnect the input stage from the finals.  
If it continues to screech, then the finals are going into oscillation,
otherwise it's probably the input stage.  Check all components that are
in the negative feedback loops... you'll probably find something open there.
--scott