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Old 20th April 2006, 12:08 AM   #1
nuvo is offline nuvo  United States
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Question Electrocompaniet Ampliwire 100

I have an opportunity to pick up an Ampliwire 100 with a shorting problem. Doing a quick take I was able to determine that the problem is from the right channel after the power supply. By any chance does anyone know if this particular model amp is plagued with problems? A few folks seem to think so - I just do not have much history on its reliability.

Thank you for the help.
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Old 20th April 2006, 10:57 AM   #2
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The Electro's I've worked on all had problems with the TO-5 pass transistors in the regulator circuit. They have some BC numbered stuff, I replace them with 2N3440/5415 types.
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Old 22nd April 2006, 02:55 AM   #3
nuvo is offline nuvo  United States
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Thank you for the information. I tested a bit further and found the right channed output transistors to be completely shorted - both parallel pairs 2SA1141 & 2SC2681 - also two 2SA1141 transistors on the driver board are shorted. I do not see visual signs of heat stress and am unsure at this point what event provoked the failure.

I seethat NEC transistors were used and would like to replace with the the same. The challenge now is to find the original OEM parts (prefered over NTE). Any suggestions?

Thanks - off to a good start.
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Old 21st June 2006, 03:19 PM   #4
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Hello nuvo

did you fix your AW100 ?

I am asking this because I am trying to fix an AW65 which is quite similar to the 100 and I am not successful so far.

Best regards

Rollo
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Old 22nd June 2006, 07:31 AM   #5
nuvo is offline nuvo  United States
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rollo22

I used a series lamp in line with the power and dummy loads for the speakers. On my unit the lamp had full illumination (shorted) so I removed both L&R channels - tested the power rails (good) and replaced the channels one at a time and determined the right channel was shorted. I found four 2SA1141 and two 2SC2681 shorted - replaced them tested the bias and found it climbing as the unit warmed. Alas the culprit - the thermal sensing transistor mounted on the heat sink. It used a thermal blanket (not good) so I tried a mica and the bias is now rock steady. hope this helps.

nuvo
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Old 22nd June 2006, 09:47 AM   #6
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Hello Nuvo

I am glad you succeded...

my case is more difficult for me, I have problems in the input stage so far.

In particular the offset at JP1 ( between the input and the output stage)
is very variable from -10V at turn on until +.6V to -.9V when warm ( to me it
looks like a temp related slow oscillation, but maybe it is normal ) .
To test I cut JP1 and put a 4K7 resistor to ground as per suggestion in schematics.

How was your JP1 Voltage settling and stability ?

I wonder if you could help me in saying (if you feel like) what are the steady voltages at some points in the circuit.

If you can, then, I would need the voltages at R5, R6, R11, R12, R13, R14 for the Input stage
and then R5, R6, R11, R12 for the ouput stage.

I understand that it would be a pain to open a working amp again but I would appreciate any help I can get.

BTW where did you find the 2SC2681/2SA1141 ?

Best regards

Rollo
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Old 22nd June 2006, 09:51 AM   #7
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Care to show what the circuit of the AW-100 looks like for us Peeping Toms ?
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Old 23rd June 2006, 12:57 AM   #8
nuvo is offline nuvo  United States
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rollo22

I will open the amp sometime over the weekend and get you the readings. Just not sure your designations match what I am working from. I got the schematic from another DIY - do not remember the name off hand but I will look it up so you can see the same print. BTW - just make sure the TO-92 transistors mounted on the large heat sink is snugged - a loose one may give you some thermal (voltage) variance.

Parts - I bought from consolidated electronics - www.ceitron.com - but he did not have all I needed and I had to buy some NTE replacements.

nuvo
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Old 23rd June 2006, 12:57 AM   #9
nuvo is offline nuvo  United States
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jacco

I tried to send the file but its too large. I got it from DIY Andypairo, check out his home page and you should be able to download.

If you want I will take a few pictures of the inside when I open it up for rollo22.

nuvo
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Old 23rd June 2006, 08:46 AM   #10
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I've managed to get the schematics from Andrea's homepage, the complete service manual is no longer present.
It would be nice if you could post the rail voltages, VCC and VDD on the AW-100 schematic.

The AW-100 schematic only has 1 pair of Toshiba 2SA1095/2SC2565 in the output stage. I remember it having 2 sets, as confirmed by Nuvo. Does the parallel output device set on the AW-100 have emitter resistors ?
1st series AW-250DMB had 12 of those ring-emitter output devices per channel.

2SA1141 are still available, sometimes for a dollar the piece, 2SC2681 is very hard to find.
Sanken 2SA1186/2SC2837 are easily obtainable replacements for the NEC devices.
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