Re: (ET) charger failure question

["David Roden" <etpost drmm net>]

Again subject to the standard disclaimer (I'm not a EE): As with many 
other 
straightforward electrical items, there are really only two failure modes 
for a transformer winding, shorted or open.  

An open in the secondary will cause either no output or, more likely in 
this 
case, reduced output, since the charger will produce half wave output 
rather 
than full wave.  

A short will usually either overload the transformer (probably tripping a 
breaker or opening a fuse), or cause low output and excessive heating.

But not always!  I've run across some interesting transformer winding 
shorts.  Many years ago I was tinkering with a friend's troubled tube 
power 
amplifier.  I don't recall all the symptoms any more, but I do remember 
noting that the wirewound hum balance control across the 6.3v tube heater 
winding was burned open.  That's odd, thunk I, and thoughtlessly laid a 
finger on one of the trimpot's terminals.  I ended up half way across the 
room.  Good thing I wasn't touching the chassis with the other hand!  It 
turned out that the power transformer's 800 volt B+ supply winding had 
internally shorted to the heater winding.


David Roden - Akron, Ohio, USA

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