Airedale S900 amp help

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Hi guys. Sorry, my first thread is a request.

Airedale S900 MOSFET amp.

It needs new caps, but works, albeit with a small amount of 100 Hz hum.

Would anybody have any info on this amplifier? I can't find a thing.
I was hoping to check the bias settings in particular, but any info would be great.

Hi, I have been working on an airedale myself, i have the contact details for the actual man who designed the circuit, they where made in Hastings Rye West Sussex, the man you need to speak to is called peter, and if you contact me i will pass you his details, when working these are great amps, they are a bit thin on the ground now, the design dates back to 1993 and they come in either 8 or 4 ohm versions, ive only ever had the 4 ohm version, it will give you 450 Rms a side at 4 Ohms, and about 300 rms a side at 8 ohms, they are fairly simple amps, but watch the rail voltages and bias settings, the output fets j200 and k1529 are expensive, before working on it remove the feed fuses from the 57 volt rail both sides, if i can help furthur please get in touch, below is some further information from peter himself.


All measurements should be done from ground = chassis. That way, if there is a break in the ground line, it should show up. The supply fuses nearest the front panel should then have -57v on them, and the +ve rail fuses, at the back, should have +57 on them.

The junction of the power fets, ie that goes off to the speaker relays should be as near 0v as dammit, as should the collector (bolt) on the class A drive (IR630). The 1ks feeding the three power fets at the back will have a couple of volts above zero on their commoned end (the other end as well, of course) and the common of the 3 1ks for the N channel power fets (front three of the 6 on each channel) should be around -2.

Very important. If the bias setting is too high the fets will overheat and 'pop'. If the bias is too low then you will get cross-over distortion. From meory, a total collector current (ie at one of the fuses, should be less than 100mA.


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Sorry for my late reply, Tim.

Thanks for the info and the contact offer, but I wouldn't like to disturb the gentleman.

I now have a 600 as well. Same amp, smaller tranny, less filter caps and less output devices.

Not finding the time to have a real look at them, but both work, and both had the obligatory burnt solder joint on the zobel resistors.

I'll try to have a good look at them and get back to you.

Thanks again. :)
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