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Old 19th July 2007, 01:02 PM   #2481
Nordic is offline Nordic  South Africa
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baaah, I forgot I had one... it works badly though... was too cheap
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Old 19th July 2007, 01:06 PM   #2482
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Also a tip for checking tansistors.

Put your meter leads over the base and emitter leads. After you have the normal forward bias voltage reading use the probe on the base lead to short against the collector lead so that you are reading biased transistor action.

If you have 600mV between base and emitter, you could read only 520mV between base+collector and emitter.
The lower the second figure the higher the gain, and you can match transistors for low voltage operation doing this.

Actually I have found that match gain holds good for higher voltages with small signal devices, but would not trust this method with power devices.


Cheers .......... Graham.
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Old 19th July 2007, 01:08 PM   #2483
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Solder sucker.

Make sure it is unscrewed regularly to remove solder, and oil the washer to keep it sucking.
Even cheap ones can be kept going.


Cheers ........... Graham.
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Old 19th July 2007, 01:35 PM   #2484
Nordic is offline Nordic  South Africa
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OK, all done... now just to clean and reinstall...

was just the one output transistor...
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Old 19th July 2007, 01:44 PM   #2485
kvholio is offline kvholio  Netherlands
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The cheap solder sucker i use comes with a pin in the center,
that pushes out the solder every time you push the piston forward.
Well, at least that's the idea

Had to check the calendar to see it's thursday, it's what working in shifts does to a person.

Loek, about possible hum-pickup in my amp: The picture is distorting, in reality there's about 6 cm distance between inputs and ac-mains plug.
Hum is undetectable in my DX, both by ear and by scope.
Temprarily bypassing the 10r groundlifting-resistors was a great way for me to find a good wiring/grounding-layout.
Worst-case setup i tried had a hum that was influenced in amplitude by gently pushing the cone of the attached loudspeaker inward

Feeling a bit sad with you Carlos about the plane-crash in Sao Paolo. A horrible accident. Well, not entirely i think.
You can only call it an accident when there's nobody to blame.

Thanks for your help regarding the layout of the Gem Graham, i must admit i was a bit lost.

Best regards,

Klaas
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Old 19th July 2007, 01:49 PM   #2486
Nordic is offline Nordic  South Africa
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I'm going to take some flak... but this is the advice given to me in a similar situation... remove mains ground from preamp circuit... let it find ground through the amp...The preamp is still in daily use.
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Old 19th July 2007, 02:20 PM   #2487
Nordic is offline Nordic  South Africa
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Waiting for wife to bring mp3 player home in an hour... but I think it is fixed... Much thanks for the company through these dark hours.....lol I'd suck as a service engineer.. this took over 6 hours....
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Old 19th July 2007, 03:05 PM   #2488
kvholio is offline kvholio  Netherlands
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You mean disconnecting the pre-amp from safety-earth ?
The pre-amp i'm using now is a class-II device, there's nothing to disconnect.

You think six hours is bad ? It once took me about 6 MONTHS
to get an amplifier working properly. But i got it working anyway

Best regards,

Klaas
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Old 19th July 2007, 03:11 PM   #2489
Nordic is offline Nordic  South Africa
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"I see" said the blind man to his deaf wife over the corner of the round table....

Lol, it has been a good tutorial... no reading could prepare me for this... and I feel a better person for COMPLETEING this, project.
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Old 19th July 2007, 04:05 PM   #2490
Nordic is offline Nordic  South Africa
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Click the image to open in full size.

Its playing...!!!!!!!!!!!!!!

Love the larger input cap... bass has more... erm .... body.
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