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i'm on a roll... the kgsshv


kevin gilmore
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Very nice s-r,  what size knob is that one?

 

 

I must tell that when I was "testing" my last build.   I reached in to move the input cable and my knuckle touched the power transistor at 450v.  Well it was quite a jolt and I couldn't help but yell "f****** h***".

 

I was wearing the phones at the time and there was a big noise in them also. There was a smell of vapourised flesh and the attached pic shows a neat crater in my knuckle.

 

I am still alive apparently but I don't intend to try it again.

 

 

post-3955-0-98910200-1408015669_thumb.jp

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It's a good thing your other hand was not resting on anything metal or conductive. Heard about a guy who use to repair old tube TV's from my tube supplier/amp builder, bloke had 1 hand on a nearby metal chassis and the other probing lethal voltages till the power arced across his hands and finger tips. He still rocking but the damage was severe enough to have damaged the nerves in his right arm. Lethal voltages beaware.

Edited by DefQon
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I need some help.

 

I completed the power board. When connected to the transformer, when I measure the top of the 100uF capacitor to ground (refer the attached image), I see -580V there. What could be wrong?

 

I get about -580V on the negative rail, and +500V on the positive rail. Bias voltage is 560V, instead of 580V. I might need to replace the zener. But first I need to figure out why the cap is showing -580V on top of it...

 

At the same time I also hear weird hissing sound. Sounds like one of the caps might blow or something. Please advice.

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Edited by kh90123
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OK it just so happened that I had a bad cap. Should complain to Mouser. The one that blew was the bad cap. Either that, or it was shorting through its metal shield. So I raised all the caps a bit to give it some air gap.

 

Now the +ve rail steadies at +505V, and the -ve rail steadies at -505V. But somehow my Pro bias voltage is at 592V, and rising. Maybe I should replace some of the zeners to get to 580V.

 

It's hitting 600V now!!!  ::)

 

Btw, the Hioki DT4282 is one of the best multimeter I have ever used. Dare I say, it's better than the Fluke 87V.

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Edited by kh90123
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OK after some time I finally figured out why my caps were blowing. The Toroidy transformer that I have, although giving out a good 16V-0-16V, doesn't give me 450V. Instead, the output on the secondaries are 487V, both of them.

 

The 680uF caps that I have are only rated to 450V. I don't recall any capacitors at good price that is good up to 500V or 600V, any suggestion?

 

Can I use capacitor of different values to replace the 680uF caps?

Edited by kh90123
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OK after some time I finally figured out why my caps were blowing. The Toroidy transformer that I have, although giving out a good 16V-0-16V, doesn't give me 450V. Instead, the output on the secondaries are 487V, both of them.

 

That sounds normal if there is no load on the transformer as the voltage for any transformer is specified at full load. At idle, you should expect 5-15% higher voltage (percentage depends on the size and core type of the transformer).

 

//UFN

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I see. Thanks. But still the pro bias voltage is hovering around 598V. Still need to change some of the zeners. When I have time tomorrow I will change one of the 150V zener to 130V.

 

The +ve is at 505V, -ve at -505V, so it looks OK now. No more blowing caps. 

 

But to be honest, caps blowing is a sight to see. The smoke erupts from the fractured shell on top of the caps, then soon you will be greeted with putrid pungent smell worse than your own worst fart.  ;D

Edited by kh90123
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