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Old 20th August 2008, 05:09 PM   #11
Mooly is offline Mooly  United Kingdom
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Hi,
Is it the same Amp as mentioned in post 5 ? If it is, the full manual is also at post 5 in that thread ?
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Old 20th August 2008, 06:07 PM   #12
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Sounds like you had a bit of an epic with the Arcam Alpha 3 in that thread! I have that manual now, which has a schematic of the Alpha, which documents +33v and -33v DC, but I can't establish what the AC output of the transformer should be to provide this.

As I say, I'm a novice at this, so I might be missing something.

Based on the serial numbers, I have an Alpha Plus.

In this thread, a 120va 2x18v transformer is used, but will 18v be high enough? I know 120va is right.

Many thanks.
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Old 20th August 2008, 06:20 PM   #13
AndrewT is offline AndrewT  Scotland
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have a look at Nuuk's site (decibel dungeon).
he details the bulb tester.
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Old 21st August 2008, 04:21 AM   #14
jaycee is offline jaycee  United Kingdom
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You can remove the suppression capacitor and it will run fine. AndrewT - I have seen these go bad, usually when hit with a big enough spike.

One thing I have thought about - check for crap on the PCB around where the primary wires connect. I'm going on what the service manual shows but the clearances around there look rather tight.

I'm also wondering if it's possible someone has attempted to convert this to 120V and forgotten to mention it. Apparently, the service manual also says the fuse should be *800mA* antisurge! The service manual shows how the primaries should be wired for 240V operation. If you don't trust the PCB, you can always rewire it using some terminal block.

I have uploaded the service manual here. It's probably all you will get from Arcam anyway.

edit: DIYaudio, isnt censoring c-r-a-p a bit overkill?
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Old 21st August 2008, 04:42 AM   #15
jaycee is offline jaycee  United Kingdom
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A 2x18VAC transformer will give 25V power supplies when rectified. In practice this reduction in voltage will be OK, you will simply lose a little output power that you are unlikely to notice in practice. You could use 2x25VAC but that would require replacing C210/C211 with 50V/63V rated parts.

It depends how much you want to spend - I would say it is worth replacing the main capacitors as they will be pretty old by now and due for replacement. I am not sure how the original Alpha One has it's capacitors wired - a picture of the insides would be useful if you can manage it.

120VA sounds about right - the most important thing here is size. Measure the old one and pick a new transformer that will fit.

Suitable RS part codes are 223-8033 for the 2x18V transformer, and 223-8049 for the 2x25V transformer. They are 230V secondaries and not 115/230V secondaries so there will only be 2 primary wires to worry about.
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Old 21st August 2008, 07:05 AM   #16
Mooly is offline Mooly  United Kingdom
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You have used a properly rated cap as a replacement haven't you. These are self healing and may not read faulty on a DVM.
Nothing else will do but you can safely remove it.
I find it hard to believe the trannys duff (it just doesn't happen really-on it's own anyway) but on the evidence so far I would suggest this.
If the trannys powered up (with secondaries disconnected) as Andrew says using the bulb and it lights then yes it's duff. Why ? If someone has fitted a 7.5 amp fuse the thing could have been cooking for ages. Does it smell ?
There is probably some underlying cause, maybe a bridge rectifier or smoothing cap, or perhap an output fault. It's strange that it did work OK at the start. And someones put the big fuse in for a reason. If it were an output fault then that would have packed up ages ago, and you would have heard it hum through the speakers, it wouldn't just have worked.
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Old 21st August 2008, 08:07 AM   #17
jaycee is offline jaycee  United Kingdom
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Yep, i should have mentioned that - it must be an X2 rated capacitor for direct connection across the mains supply!

If push comes to shove, leave it out - it will just make some interference when you switch it on/off. A better place for the capacitor wouldve been across the switch contacts IMO.
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Old 21st August 2008, 08:08 AM   #18
AndrewT is offline AndrewT  Scotland
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Hi,
the advantage of using the bulb tester is that it stops the equipment blowing up and gets the circuits live, enabling measurements to be taken.

If only the transformer is coupled up then the first check is input and output voltages on all the windings.
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Old 21st August 2008, 08:09 AM   #19
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by jaycee
Yep, i should have mentioned that - it must be an X2 rated capacitor for direct connection across the mains supply!

If push comes to shove, leave it out - it will just make some interference when you switch it on/off. A better place for the capacitor wouldve been across the switch contacts IMO.
no Jaycee.
You are referring to two different capacitors with different purposes.
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Old 21st August 2008, 11:20 AM   #20
jaycee is offline jaycee  United Kingdom
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Yes, in the second case I was referring to supressing sparks across the switch contacts, which wear away the contacts and create switching noise.
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