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Old 1st November 2009, 11:44 PM   #1
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Default Troubleshooting the decware se84 kit

i received the decware zkit1 a few weeks ago.

schematic - http://www.decware.com/newsite/SE84CDIY.pdf
site notes - http://www.decware.com/newsite/SE84CDIY.pdf
assembly instructions - http://www.decware.com/newsite/SE84CDIYINSTRUCTIONS.pdf

i have the board populated and the transformers and panel mounted components connected to the board in a temporary fashion.

yesterday i turned it on for the first time and tested the voltages at the required points and found all the voltages within the suggested ranges. however there were two problems.

1. one or both output transformers were making a high pitched continuous noise that didnt stop until i turned the amp off.
2. there was a peculiar smell coming off of the board. it seemed to be localized to the two big resistors rated 5W. some people i spoke with said it was the oil from my fingers burning off of the resistors. it smells like oil burning however i would like to be sure that i am not cooking anything here.

The voltages were as follows,

A – 343.5V
B – 300.1V
C – 8.64V
D – 3.061V



after letting the amp sit for a few hours i turned it on again.

the output transformer noise was gone. the smell and the heat were still there. the voltages at A and B have however, dropped to 327V and 286V respectively. the voltage at C is at 10.1V and D remains constant at 3.06V.

also the 2x1.5kohm and 2x2.7kohm resistors are both reading at 960ohm (all 4 are reading 960ohm). all other resistors test at the values they are supposed to be. i have gone over my solder joints and re-flowed solder to any joints that looked suspicious.

lastly, there is almost no volume with fostex 127e drivers until the volume pot is turned about 80% of the way. then the volume kicks in and there isnt much range to it. it goes from inaudible to fairly loud to the loudest (which isnt very loud) very quickly. so hard to control the volume.

i have sent 2 emails to the designer steve deckert at decware already and am awaiting a response from him. i figured i would post here as well and put the question up to all you fine people. any thoughts or comments would be much appreciated.

thanks,

cj.

ps. the entire case is wooden.
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Last edited by crappyjones123; 1st November 2009 at 11:59 PM.
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Old 2nd November 2009, 12:09 AM   #2
chrish is offline chrish  Australia
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Those output transformers look like Edcors. In the amps I have built, when I put a signal through the amp, I sometimes get a mechanical squeel from the transformers that changes pitch when I change the frequency of the signal generator... Sounds like that problem has gone away though. As for the measured resistance values, 1.5K in parallel with 2.7K will give you 964 Ohms, so your measurements of those resistor in circuit, look right. Can't comment on rest at the moment, stepping out the door to work...

Good luck though,

Chris
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Old 2nd November 2009, 12:56 AM   #3
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1.5k in parallel with 2.7k = 964 so that explains that right. Voltages seem about right.

But it does sound like something is not quite right, the sound from the transformers could have been caused by oscillation.

The manual showns the tube sockets mounted on the component side. You have yours mounted on the other side which means that the tube pins are backwards.

Hopefully no permanent damage (ie the smell was oil)

dave
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Old 2nd November 2009, 01:10 AM   #4
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the components can be mounted on either side, however the sockets and the volume pot must go on the side with no printing. the tubes and the volume pot are on that side in my build. the reason the components are on the same side as the sockets are because its mounted on TOP of a board. for chassis mounts, it would be mounted underneath. much like the following gentleman's build.

Jet5
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Old 2nd November 2009, 01:23 AM   #5
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Fair enuff...

dave
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