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Luxman L3 38VDC On Speaker Output?
Luxman L3 38VDC On Speaker Output?
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Old 11th January 2019, 04:56 PM   #61
Apasacii is offline Apasacii
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Roger! Thanks for the tips.
R416 and R417 aprox 0.3
Q403 - 2sc2229 is new
Q404 - 2sc1740 rd is faulty - bought 2sc2240 gr 3c
Q406 - 2sa965 0 seams ok - bought 2sa1013 y
Q405 - 2sc2235 - i have a new one
Q407 & q408 seams ok.
Can u confirm me if replacements that seller recommended me are suitable ? Ty. And the point for the bulb to connect pls.to be safe.
Thanks !

Last edited by Apasacii; 11th January 2019 at 04:58 PM. Reason: Fault
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Old 11th January 2019, 08:39 PM   #62
Mooly is offline Mooly  United Kingdom
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Luxman L3 38VDC On Speaker Output?
2SC2240 should be fine for Q404.

2SA1013 should be OK for the driver.

The bulb goes in series with the live mains supply to the amp. One easy connection point (but its up to you to make sure you are safe with the connections) is to remove the mains fuse from the amp and to solder a bulb across the fuse holder. So the bulb takes the place of the fuse.

Powering Your Radio Safely with a Dim-bulb Tester

Also turn the 330 ohm bias preset to MAXIMUM resistance before switching on. This will set the bias current to minimum. So the preset needs to be turned to make it appear as a 330 ohm resistor.
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Old Yesterday, 08:46 AM   #63
Apasacii is offline Apasacii
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Thanks ! Back with result, which is very good i think.
1. Checked all resistor to be sure everything is ok (values are usually a little bit lower)
2. Checked q401/q402
3. Replaced q403,404,405,406 with same or equivalents from above
4. Replaced 1A fuse with 75w bulb
5. Powered up

Result :
1. Bulb lighted shortly when started up then went off - removed bulb and started to measure
2. Voltage on output (aprox 0.01-0.04v on both channels)
3. Made a test with signal and a apeaker on both channels (low volume cause radiator for q407 and q408 is not mounted) - both channels were up and running.
4. I made a few measurements because it seems to be a difference in voltages between the two channels:
ECB
outputs : q407a -0.04/41.2/0.43 q407b +0.25/41.1/0.4
q408a -0.04/-41.3/-0.04 q408b -0.04/41.3/-0.04
q405a 0.04/41.3/1.0 q405b 0.04/41.3/0.9
q406a -0.4/...../-1.0 q406b -0.4/...../-1.0

where "a" was the problem channel
q407a has the collector pin broken and soldered (don't know if it's a problem but i'll change the outputs with originals or some more suitable when i find some).

Another possible problems:
1. main voltage - 41V ? isn't too high ?
2. when powering off , voltage (aprox 10v and slowly dropping) appears on both channels.
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Old Yesterday, 09:47 AM   #64
Mooly is offline Mooly  United Kingdom
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Luxman L3 38VDC On Speaker Output?
That all sounds basically good

The two important checks are:

1/ That there is less than 100 millivolts across the speaker terminals. It will probably be a lot lower than this but 100mv would be an upper limit.

2/ That the bias current of the amp adjusts OK. This is set with NO speakers or signal. I would aim to get this at around 6 to 8 millivolts as measured across either of the 0.33 ohm resistors. That will give a current of around 25 milliamps at most.

Seeing a falling voltage at the output is normal and is caused by the supply rails falling as the reservoir capacitors discharge. That causes the amp to develop a high DC offset as it 'loses control' due to the low supply voltage. Once a speaker is connected that voltage will fall very quickly.

Normal mains variations won't cause a problem, 41v is fine and would fall anyway when the amp was under load.
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Old Yesterday, 09:12 PM   #65
Apasacii is offline Apasacii
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Roger! For the outputs :
Sb686/Sd716 are 12 mhz
What do u recommend ? 20 mhz or 8 mhz ? Bd249/250 are 3mhz (installed ones).

I've just replaced the el.caps from the other channel.
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