[Amps] Need Diagnostic help

Tue Aug 17 19:34:15 EDT 2004

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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