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Why you should power up your electrostatics first: A Warning!

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It was late one night so I was listening on headphones and switched off my ESL-63 and 405 power amp (or so I thought).  Much later when I took the headphones off I realised that the left speaker only had been powered off so lowish level music had been going through it for half an hour or so.  The next day to my horror revealed the awful truth: the left channel was completely silent- the  minus volt fuse had blown and a replacement immediately blew again but fortunately the speaker was unaffected.  As I had worked on the 405 before, I managed to locate the dead component, one of the MJ15003G power transistors (see photo) had melted inside and caused an emitter to collector short circuit.  No other component had failed although a resistor needs replacing as it looks a bit cooked.  So a cheap £6.15 fix, but not if it has to go to the repair shop.

I hadn't really appreciated that the ESL presents a short circuit to the amp when the mains power is absent! So everyone beware although I believe that if there is no power is present for just a few seconds, it won't matter, but please don't try to find out.

I've had the ESL63s for a few years so you have to be a bit careless to do this.  I hope that my tale is a warning to be careful to other electrostatic speaker owners.

Dead Transistor.jpg

Edited by aggers
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