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In article <17u3gbINNfuv@darkstar.UCSC.EDU> haynes@cats.ucsc.edu (Jim Haynes) writes:
>From: haynes@cats.ucsc.edu (Jim Haynes)
>Subject: Weird Science?
>Date: 31 Aug 92 21:38:19 GMT
>
>I've got this circuit which consists of
>   8:1000 ohm input transformer feeding
>   DIP bridge rectifier feeding
>   base-emitter junction of a transistor.
>The idea is to connect the 8-ohm input to the output of a radio or
>tape recorder and turn on the transistor when there is some signal.
>
>It works fine, at first.  After it sits for a while, turned off, it
>won't work.  Then I disconnect one of the secondary leads from the
>transformer, observe with an AC voltmeter that there is voltage there,
>and reconnect it.  At that point it starts working again.  I've been
>through several cycles of this - probably I'll connect the transformer
>with a clip lead to make it easy to get it going until I get to the
>bottom of it all - but does anybody have a clue what is going on here?
>Intermittent connection somewhere down inside the transformer?  Is there
>some latchup phenomenon with DIP bridge rectifiers?
>-- 
>haynes@cats.ucsc.edu
>haynes@cats.bitnet
>
>"Any clod can have the facts, but having opinions is an Art."
>        Charles McCabe, San Francisco Chronicle

Most likly the problem lies in the bridge rectifier, you need to use fast 
recovery diodes, normal bridges are design for power line, and can not 
perform at sound frequencies. They behave kind of short cicuit, then 
junction temperature increases, and that may be the cause of the Weird 
Science.




Peace and Prosperity!
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