Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!csd4.csd.uwm.edu!info-high-audio-request
From: cti1!rmorss@uunet.UU.NET (Richard Morss)
Newsgroups: rec.audio.high-end
Subject: Re: Miscellaneous Comments
Message-ID: <10055@uwm.edu>
Date: 8 Mar 91 13:38:20 GMT
Sender: news@uwm.edu
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Approved: tjk@csd4.csd.uwm.edu
Originator: tjk@csd4.csd.uwm.edu


JWB@SLACVM.SLAC.STANFORD.EDU writes:


>In article <9903@uwm.edu>, Daniel_Rai@ub.cc.umich.edu says:
>>
>>     A Dyna Stereo 70 keeps blowing the main fuse
>>     seconds after powering up.  The tubes are fine,
>>     and they all light up before the fuse blows.  What
>>     could be causing this?

>(Much deleted)

>You say the tubes are fine, but are you sure? I had a similar problem
>with a Scott Amp after driving it to hard. Turned out to be the rectifier
>tube for the power supply. It too lit up prior to the fuse blowing.

>Just a thought...

>John Beach

>[The 5AR4 is allegedly notorious for heater-cathode shorts, according to 
> a retired technician of my acquaintance.  -tjk]
If the replacement 5AR4 doesn't solve the problem, you need to start checking
all the capacitors in the amp.  A system this old probably has a leaky
power supply filter cap at best.  If you have the original assembly manual,
there should be a very detailed checkout procedure right after the last    
assembly instruction.  My memory doesn't go back that far, but, as I recall,
they have you plug the thing in the wall with all the tubes removed to
check for shorts.

In any event, replacing the PS filter cap should do the job.