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Re: [Amps] Need Diagnostic help

To: amps@contesting.com
Subject: Re: [Amps] Need Diagnostic help
From: Alek Petkovic <vk6apk@eon.net.au>
Date: Wed, 18 Aug 2004 07:34:15 +0800
List-post: <mailto:amps@contesting.com>
Tom,

I have a home brew 2 x 3-500Z amplifier, with 2kV and 3kV DC taps, which displayed similar symptoms. At turn on and after that it would emit a buzzing and arcing sound.

The amp is at my holiday house so it gets very little use. I thought it was a problem with the filter caps in the ht supply, so I ran the amp for 24 hours on the 2kv dc setting to try and reform the caps.

After that period, I switched to the 3kv dc position and everything seemed ok. No more buzzing or arcing.

The next morning, I turned on the amp in the 3kV position and there was a sharp bang from inside the amplifier. I hurriedly switched it off and then had a shower and put on some clean underwear.

I lifted the top cover of the amp and found that the plate coupling cap had suffered major trauma. There was a small shot hole from one side through to the other. It was a 3" diameter, 1000pF @ 7.5kV, 20kVA ceramic doorknob type. It was obviously not meant for the kind of service I was asking of it.

A call to Rudi from Emtron resulted in a nice new capacitor which was meant for the job, residing in my amp. I don't anticipate any more trouble in that area.

Check your plate coupling cap or disconnect it to see if you have a similar problem.

73, Alek,
VK6APK



At 12:59 PM 17/08/2004, Thomas Hix wrote:
I am my wits end with a recurring problem, and I am hoping maybe some of you may be able to help me.
The last two amps I have had both seemed to be arcing internally somewhere.
The first amp I had problem with was an Emtron DX2SP......The high voltage meter would deflect downward slightly and there would be the sound of an arc inside the amp......you know a buzzing sound that sounds just like a small arc to ground.
We took the amp apart and for the life of us we could never find an arc......I sent the amp to a friend who is a major repair shop for amps and rigs, and it would never do it at his shop.....never.
We got it back, and it started doing it again here.....slight deflection of the high voltage meter and the buzzing sound inside the amp.
I got disgusted and sold the amp......and then I bought a like new Alpha 77SX with 2 8877's.
I used it a few weeks and no problem.....I was getting about 4kw out with 100 watts drive (into a dummy load of course) and the amp just worked wonderfully.


Then a couple of weeks back, it started doing the same exact thing as the Emtron DX2SP had done.......the high voltage meter would deflect and the arcing sound was there just like in the Emtron DX-2SP.....I had the Alpha taken to my friends shop.....He took it completely apart and checked everthing....every wire....every connection for any break or sign of arcing.....nothing....he even checked the oil filled capacitor.....it was fine.... and he ran it for 3 weeks, and he never once had any sign of arcing or any meter deflection......nothing....once again, the amp ran beautifully at his shop and he used it on the air for 3 full weeks.....nothing.

He brought it back home to me Sunday......we hooked it up, and there it was again......it was once again making the arcing/buzzing sound inside the amp, and every time it did it, it was making the high voltage meter deflect downward at the same time the arcing/buzzing sound would happen.

OK that is 2 different amps that had the same exact symptoms while at my location hooked to my 240 line.......both amps were making the arcing/buzzing sound inside the amp and both were showing a downward deflection on the high voltage meter.......both amps worked wonderfully with no sign of arcing/buzzing and no high voltage meter deflection when hooked up at my friends shop.

That can only bring me to one conclusion.....there is something wrong with my 240 line?????

My question to the group is this......Could a problem with my 240 line cause these amps to make an arcing/buzzing sound inside the amp that sounds just like something is arcing to the cabinet without this actually happening.....I can see where if I have a bad connection or something like that inside my breaker box or even on my 240 wall outlet I might see a deflection on the high voltage meter, but could that also cause there amps to make a noise like something is arcing inside the amp???

I tell you this has really got my goat......I cant imagine what a bad 240 volt connection could do to there 2 amps that would make an arcing sound inside the amp, but there is no arcing to be found??? We have looked inside the amp with all the lights out at night when any arc should show up, but we can not see any kind of arc.....so I am thinking there is some component inside the Emtron DX-2SP and the Alpha 77SX that will make that kind of arcing sound.....even though it does not arc......when it loses either ground or voltage on the 240 line for a split second.

I am a handicapped person so I cant check out my 240 line myself. I live in an old house and there is no telling what can be wrong with the 240 line.....but I need a starting point....some things to look at when I do get someone to come and see if they can get this thing figured out.

I am open to any suggestions and or diagnosis.......I NEED HELP! This is driving me nuts.

Thanks!!!
73
Tom......W4TH


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