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Quad current dumping amplifiers

Chops54 said:
Are these any good Robert?

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Those look right for the stock 306.
However I'm going to be a heretic and suggest that you use Panasonic 6800uf parts.
The 306 is tiny and was an 80s design. Caps have shrunk and got better since then and while we cannot be certain, I'd bet money on the original cap value being used because they simply couldn't get anything larger in the case.

It also gets hot in a 306 so there should be some benefit from the higher temp rating of the panasonic part in terms of working life.

I use these in mine and in the few I've serviced for folk:

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=339-7060
 
Well I've bought one. £160 for a gunmetal Mk 2. Looks to have been recapped in 1996 so I'm guessing it will benefit from another. It should arrive on Thursday so I'll report back once I've cranked it up.
 
Hmm. Shame. You'd want to be picking that up at £50-100 to finance the repair. Are you sure it's the amp, not a connection issue?
 
stevec67 said:
Hmm. Shame. You'd want to be picking that up at £50-100 to finance the repair. Are you sure it's the amp, not a connection issue?
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Totally. Internal fuses are fine too. Seller claims it was fine when he shipped it. Maybe it was, but it isn't now. Plus I wasted a day's leave waiting for UPS to show up.
 
I have known the fuse holders on the boards fall to bits, therefore fuses not making contact. A friend replaced the big smoothing caps on his working 405. It did not work after on one channel. He thought he had done some wrong wiring, it was just the fuse holder. Touching another fuse holder in this amp, it fell apart as well. Metal fatigue/ corrosion.
 
The seller has agreed to take it back which is cool, but it may be the fuses after all. I hadn't initially noticed that there were two sets of internal ones. However, having changed them all, I now can't switch it on without blowing the main fuse (2.5 A/250V). Is this a common problem when powering straight from the mains rather than via the pre? Can't see why it should be and I didn't initially have this problem. If this is easily fixed, I'd rather hang on to it that send it back.
 
I wonder, is the amp set for the correct mains voltage? If set for say 110V and run on 230V the mains fuse would likely blow. 405's and possibly early 405-2's had an voltage adjuster on the back panel. later models had to be hard wired inside for the different mains voltages.
 
Radfordman said:
I wonder, is the amp set for the correct mains voltage? If set for say 110V and run on 230V the mains fuse would likely blow. 405's and possibly early 405-2's had an voltage adjuster on the back panel. later models had to be hard wired inside for the different mains voltages.
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This one has an adjuster on the back - it's correct.
 
When you first tested one channel was working. I wonder what has happened. Are your speakers/ connections OK, no shorts?
 
405 and 405-2 have crowbar protection. it is possible that this has actuated due to a fault on the board(s). The -2s have this protection build in to the amp boards. 405 had a small pcb (after thought) mounted on the rear of the speaker connections.
 
Any signs of the two big power supply capacitors bulging/ leaking?

The amp modules can be repaired, Quad still have an excellent (and reasonably priced) repair service. You could just post the boards to Quad if they are faulty.

You could get a quote from Quad and ask the seller for a partial refund. Saves unnecessary postage costs for a heavy amp. You both win if he agrees. Especially worth doing if amp is cosmetically very good.

There are some clone 405 (not 405-2) boards on e bay, they look good and are cheap, but they don't include the small crowbar protection board (I think).
 
Radfordman said:
Any signs of the two big power supply capacitors bulging/ leaking?

The amp modules can be repaired, Quad still have an excellent (and reasonably priced) repair service. You could just post the boards to Quad if they are faulty.

You could get a quote from Quad and ask the seller for a partial refund. Saves unnecessary postage costs for a heavy amp. You both win if he agrees. Especially worth doing if amp is cosmetically very good.

There are some clone 405 (not 405-2) boards on e bay, they look good and are cheap, but they don't include the small crowbar protection board (I think).
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Nothing obvious. I'll send it back. I bought it as working and it isn't.
 
The internal fuses protect the positive and negative rails of the individual boards and the holders are very close together. I have seen faulty boards with fuse holders touching, which will certainly cause the main fuse to blow, possibly along with the output trannies/drivers.
 
I must agree with Radfordman on this. If the amp is cosmetically good, why not send it back to Huntingdon for service and agree, perhaps, that the seller takes one-third of the service cost as a reduction from his sale price?

Then you end up with an as-new 405-2.
 
graham55 said:
I must agree with Radfordman on this. If the amp is cosmetically good, why not send it back to Huntingdon for service and agree, perhaps, that the seller takes one-third of the service cost as a reduction from his sale price?

Then you end up with an as-new 405-2.
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Or save money and just send power amp boards.
 
Well, I'd have the whole thing checked over, but I know efall about how amps work!!

And, if John's in Norwich, he could book it in for service, and collect later in the day.
 
I think I'll just return it. I have very little time to mess about with half working amps. I'm not in Norwich anymore, I'm facing my PhD viva next week, I'm trying to get some good post-doc collaborations going and I'm getting married in a couple of months. No time!!
 
Well, mugger me, John, good luck with your viva voce next week. Try to sneak in buying a (working) Quad amp between that and getting wed.

Good luck, mate!
 
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