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Restoring an AU-X1

Hyperion said:
I am now wondering if the pre-drivers 2SC2071 // 2SA939 would be better replaced with MJE340 // MJE350 and 2SC2238 // 2SA968 drivers with 2SC4793 // 2SA1837 - these replacements don't have a metal tab collector, but I can get around this quite easily. Also I want to use replacements where there is absolutely no chance of counterfeits.

Note that I have damaged pre drivers and drivers - so I need to replace both pairs with complementary replacements. - any thoughts?
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According to many DIYers, 2SA1837 // 2SC4793 are fine choice for that part of circuit. Some say also that 2SA1930 / 2SC5171 perform even better.
 
Thanks Karl, I came across 2SA1930 / 2SC5171 being suggested as a good replacement for the originals, however I am happy with 2SA1837 // 2SC4793 in that position now.

Mouser stocks the 2SA1930, but no longer stocks it's complement the 2SC5171. :(
 
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I found 2 more failed 390 ohm resistors, on the other driver board, found to be ~50K ohm. :(
 
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Ronito6 said:
Do you refer to the resistors at positions 36 and 37 on the driver board?
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Correct, they are behaving a hell of a lot like fuse resistors (and they look like them too) but according to the schematic they are ordinary resistors. Harold said his R36/37 'fell apart' they were so knackered!
 
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Yes. I have had the chance to dig into two AU-X1's. One a version from 1979 the other (running version) from 1980. The resistors at positions 36 and 37 were shot in both...all shot.

I upped the wattage of the replacements I installed in mine. Probably not wise...but so far my X1 is still singing along.

I wonder why that position is so brutal to resistors?
 
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Ronito6 said:
I wonder why that position is so brutal to resistors.
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Good question Ron, I can't see why it should be so, I have checked many other resistors in that area and they all show good, I'll be keeping a close eye on this from now on. I replaced mine with ½ watt metal film types, stood up on ceramic beads, just in case...
 
I got the other driver assembly reconditioned, and installed - just running a bias and DC offset stability test on it now - looks good - seems to be exactly the same as the other one now. :smoke:
 
AUD101 said:
John - where's the pic's of the completed boards?
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See post #25 - the only difference from what's actually in the amp now is the driver transistors on the heatsink are different and D101 (top RH corner below 2 resistors) has been changed - everything else looks exactly the same.

I will be taking the driver assemblies out again, so if important to you, I can take new pictures then. :)
 
No further progress, apart from having finalised and placed another parts order which I have only just received. :thumbsup:
 
Here is a little teaser for you...

These are the components removed from the 2 driver boards and the 2 MM head amp boards only. 7 (or 8?) further boards are untouched as yet.

IMG_2062a.JPG
 
First time I've seen these replaced on an X1.
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What is replacing them?
 
I had a blown one, (o/c B-E) so I had to replace it and its complement, and felt I should do the same on the other channel to 'even it up' - so 3 good ones there.

2SC2071 = KSC3503, and 2SA939 = KSA1381

Suggestions for better replacements always welcome, providing there is zero chance of counterfeits.
 
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Finished MC Head Amp board (left) next to 'stock' board, (right).

IMG_2063.JPG

Sharp eyes might see something of mild interest. (no, the electrolytics are not in the wrong way round :)).
 
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