re: KAT34 problem

[hotvalve]

Hi all,

I wondering if any of you good folks could assist?

I have a KAT34 kit that I built in the early 2000's. Its been my pride and joy since then and has never really given me any issues apart from having to replace a few bulging electrolytics about 5 years back.

The amp has been packed away for the first half of this year as we have been doing some decorating. I finally got the chance last Friday to plug everything back in and fire it up in addition to a new turntable and phono preamp.

Everything sounded great for the first 30 mins. One of the records ended and after about 10 mins there was a loud speaker buzz. I dived across the room for the off switch and could see lots of blue arcing within the rectifiers (I think it was the rectifiers but to be honest I was in such a rush to get to the off it may not have been!). After turning off there was the smell of burnt components and a puff of smoke from the chassis suggesting something had gone into meltdown.

Anyway...I have had the house upside down looking for the schematics and build instructions to no avail. I've also done a search on the forum but not been able to turn up any schematic details so far.

So...

- would anyone out there have a scan of the original build instuctions with schematics? , from memory the Kit34 was the same schematic but with additional inputs and volume control?

- I not done any post mortem yet as far as opening the amp up to look for damage but if the sparking was in the rectifiers would anyone have any clues as to possible cause?

Any suggestions would be really helpful. Its been a fantastic amplifier and I'm keen to get it mended as for the limited time it ran with a turntable it sounded even better than it did with CD's.

Regards
Stu

[bob orbell]

Well Stu, it sounds as if something has gone short circuit after the 5U4 rec. valves, you need to open up and see if you can locate the burning, it will be worth switching on again just to see if the 5U4's heaters are still working, you should be able to see if they are within about 5 seconds, then switch off, I would consider looking at C5, the large capacitor 120 or 82 uF 500 volt fitted in a clamp near the choke, and also the choke, check also C1-2-3 and 4, 100 uF 450 volt on the power supply board, although both pairs will need to have gone short to give you this problem. BOB

[hotvalve]

Bob, many thanks for getting back to me so quickly its much appreciated.
Ill do as you suggest and start some investigation and see if i can find that short.
Do you know if the schematics are avalible anywhere, google is drawing a blank and this would help me no end when i break out the multimeter.
Thanks again
Stu

[bob orbell]

Many members and most Moderators will have the information you need, however, because of a copyright that now belongs to our Administrator (Matthew), you may need to ask his permission, so, either ask Matthew or any of the Moderators, Colin, Richard or John. BOB

[Greg.]

Hello Stu,

I have the build instructions and the schematic you require. On this thread you will see I have been collating such information to forfil exactly your kind of purpose. http://www.world-designs.co.uk/forum...ead.php?t=7464

At present I do not have Matthew's (his interlectual rights) immediate authority to post them to you. Please PM him or better email him through the World Designs website http://www.world-designs.co.uk to gain his authorisation for me to release this material to you. Once authorised, please PM me a copy of the authorisation and your email address and I'll get what you need to you soonest.

[Greg.]

I've had a response from Matthew. Files have been sent to you, Stu.

[Richard]

Hi Stu,
Rects usually fail at switch on but consider fitting the balancing resistors suggested in the FAQ,
http://www.world-designs.co.uk/forum...ead.php?t=3859
It may be an el34 cathode bypass cap C15,16,17,18. If one goes short the valve draws excess current which may arc the rects. Hopefully all will be obvious upon inspection but I'd replace all the electrolytics anyway at that age