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Another AU-919

Hyperion

Hyperion

Roobarb & Custard
Subscriber
Yesterday I had the pleasure of meeting another UK AK member Multimode (David) - he delivered his cherished AU-919 to me for reconditioning.

It is a very clean example, at least 9½ out of 10 for cosmetics, and completely untouched on the inside. The icing on the cake is - original output transistors. :thumbsup:

It is on my bench now, I'll be reconditioning the driver board first before any listening test, as this may risk the precious OP transistors. I'll post up some pictures in due course, but as I have already provided copious pictures for the 2 AU-919's I have already restored, I'll limit this to a few 'before and after' shots. :thumbsup:

Watch this space... :king:
 
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Leestereo said:
That AU-919 is in good hands.
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I know! I'm very careful as to who I let free with such precious objects. It's the first time in 36 years that anyone but me has been allowed near it!

I very much enjoyed meeting John and being taken on a tour of his playback and test equipment. :)

I've also enjoyed following your own refurb of a 919, Lee. Much of it was over my head, but still highly fascinating - and incredibly well presented too. It's so addictive that I've now read through it three or four times. :trebon:

David.
 
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I always wanted to have a AU-919. So impressive.
It's going to be one heck of a amp when complete.
 
I started stripping the old parts off the driver board today, and I found one electrolytic capacitor that when I removed it one of the legs fell away as if it had been eaten through somehow - also it had a suspicious black mark underneath it (C61). It was in a 'hot spot' so I think it had failed and vented out of the bottom. When I fit the L&R replacements I'll do my usual trick of using slightly longer than normal leads for these two - C61 & C62 - to be able to swing them away from the very hot resistors nearby that cook them mercilessly. :)

As usual I am forced to un-solder wire jumpers and remove other components to properly clean the glue off, fortunately the glue is not the worst I have come across in difficulty of removal, or extent - so its all good. :thumbsup:
 
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John,

I'm not aware of the full part played by the driver board (though it's probably obvious to those with an audio-electronics mind). Could the broken capacitor have been the cause of the distortion suffered on the left channel, which I avoided by using Jump?

I put up with this problem for a long time, but it eventually gave me the push I needed to have the amp overhauled. I wasn't aware of the black flag weakness back then, otherwise I'd have acted very much sooner!

David.
 
Well, interestingly it was in the Left channel, but at the moment I can't see a connection between use of the Jump Switch and that particular capacitor.

As for the function of the driver board, it takes the output of the pre-amp (or source) and as the name hints, increases the levels enough to 'drive' the output transistors. :rockon: :D
 
Deploying 'Jump' always and completely avoided that particular distortion. But you may find the cause elsewhere as you progress!

Am I right in thinking that Jump bypasses the main amp, so that the feed to the speakers is supplied only by the pre-amp stage? That was my thinking, right or wrong.

With apologies for trying to discuss something of which I know almost nothing! :(
 
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