KAT 6550 dead....!! - World-Designs-Forum

LSfarzo · #1 28th May 2009, 11:52 AM

Hi all,

I'm very distressed because my 6 years old KAT6550 is experiencing a problem I cannot manage and so I decided to post this thread to ask an help.

My KAT6550 has been modded with high quality resistors, AN silver coupling caps, new and better 6550, NOS phase splitters and by swapping the famous C5 with a Black Gate WKz at 100uF 500v. Moreover it has the bridge rectifier modded following the advice of this forum with a fast diodes bridge. It sounded great !

Since from its birth I experienced the blow fuse problem but using a 2.5A slowblow fuse it happened very rarely and so I lived well with it.

Two weeks ago I moved and since from the first time I turned it on in my new home the fuse blowing began very frequent.
Two days ago my fuse literally exploded with a flash while I was trying to switch the KAT on.

I tried different slow blow fuses but they all flash/explode. So I tried a 5A (!) slow blow fuse. The KAT turned on regularly but after some seconds the fuse blows (quietly) and it happens every time I try to turn it on again.

Do someone can give me some hints?

Thank you very much
Luca

Mike G · #2 28th May 2009, 12:32 PM

HI,

You maybe want to look at this thread. I've fitted inrush / surge limiters as suggested by Dr John, and they have cured the fuse blowing problem on my KAT 6550. Mine's been trouble free for several years now.

http://www.wduk.worldomain.net/forum...inrush+limiter

Regards

Mike.

Chris · #3 28th May 2009, 01:01 PM

It seems the move may have something to do with it? ie it may have had a knock and caused some damaged inside..or your new home has now a higher voltage, above the 230v.

I would have good look inside, and may be check all the connections and soldering points....looking for any signs of stressed parts, ie blacked up resistors or any smell of burning...

It's worth making sure it's not a fault before putting in higher value fuses..

Richard · #4 28th May 2009, 02:02 PM

Hi Luca,

You say the fuse flashed. The fuse is fairly well hidden so I wonder if it was the rectifier valves that flashed then you found the fuse had blown?

If you haven't fitted them I strongly recommend the balancing anode resistors in the FAQ http://wduk.worldomain.net/forum/showthread.php?t=3859 and mentioned in this thread also, http://wduk.worldomain.net/forum/showthread.php?t=5180

If the 5A fuse blows after a little longer it could be the rectifiers getting old so try new ones. If it still blows it will be due to drawing too much current which could be anything including a shorted mains tx primary, failing psu caps, etc.

My first moves would be the balancing resistors and a new set of rect valves.

Rich

Mike G · #5 28th May 2009, 02:16 PM

Agreed, increasing the fuse rating is not the answer. A good visual check should be done first and then if the amp stays on long enough, i'd check the reference voltages.

If it blows immediately on swith on, it sounds like a dead short that could be caused by a stray wire during the move or a failed component., If it stays on for a few seconds before blowing, this could be a component that is beginning to fail and drawing a higher current than usual due to it's characteristic changing.Mike.

LSfarzo · #6 28th May 2009, 03:21 PM

Thank you all for this replies.

The first thing I did yesterday was to check that all components looked fine, and so did them!

I check the soldering points (many !) and all seemed fine.

So I will try to use the Inrush power limiter to the 5u4Gs before trying to change them to some new ones.

I read I should use 47R resistors. Would someone be so kind to tell me their wattage; 7W ?

Otherwise I will try to check some voltages in the short time I have between the start and the death when I use a 5A fuse... having a so short time I guess if you have some hint to the place worth to test before others.

Best regards,
Luca

Richard · #7 28th May 2009, 04:05 PM

Hi, The inrush limiter will only do that; limit the inrush at switch-on. If you're blowing 5A fuses after a few seconds it will not be that.

Fit the balancing resistors which will protect the rects by balancing the current through them and limiting the inrush current.

Then change the rects which may be old and drawing too much current.

I wouldn't risk new rects without the balancing resistors. Some work, some will flash over. Yes 47R 7W wirewounds.