Replace Mark Levinson ML-2 with MJ15024/15025 need help - diyAudio
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Old 15th April 2006, 06:46 PM   #1
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Default Replace Mark Levinson ML-2 with MJ15024/15025 need help

Dear all,

I have just replaced all the transistors(2N5686 and 2N5684) on my pairs of Mark Levinson ML-2 with MJ15024 and MJ15025(matched). The result is pretty stable, I am now trying to adjust the bias voltage to .56V(1A current to each transistor) as instructed by the service manual available on the web. But both units seems very hot, I cross check the bias voltage of other ML-2 with original transistor and they are around .4V....am I setting the bias voltage too high? Anyone have some idea this replacement?
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Old 15th April 2006, 06:58 PM   #2
Netlist is offline Netlist  Belgium
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Did you measure both amps bias'ses when cold?

/Hugo
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Old 15th April 2006, 08:32 PM   #3
AVWERK is offline AVWERK  United States
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From memory, the 5686 combo are rated at 30 amps each and the 15024 combo at 15 amps each tranny.

Not sure if this has any effect with the original bias level?


David
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Old 16th April 2006, 01:36 AM   #4
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Quote:
Originally posted by AVWERK
From memory, the 5686 combo are rated at 30 amps each
50 amps.

Those are two tough transistors.
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Old 16th April 2006, 07:27 AM   #5
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So this means 1 amp current to the MJ15024/MJ15025 will not do any harm to the transistors?

Just compare with 2N5686/84, if the manual said the bais is .56V what voltage should I tune for the bias for MJ15024/25?
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Old 16th April 2006, 08:04 AM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
are you saying that you have replaced 50A transistors with 15A transistors?

Or have you put in three times as many pairs?

Why do the 50A pairs need replacing?
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regards Andrew T.
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Old 16th April 2006, 05:29 PM   #7
djk is offline djk
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"Why do the 50A pairs need replacing?"

It's a 20W class A amplifier, after 30 years it could have just worn out and failed.

The MJ1502X parts should be close enough to work.

I would look at the amp with a scope, the new parts are a bit faster.

Generally, 1A per device (2A for the pair) is enough bias for class A in a push-pull amplifier to do 32W into 4 ohms (64W at 8 ohms).
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Old 16th April 2006, 05:39 PM   #8
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Thanks for all the help.

It is because serving over 30 years, those 2N5686/84 were out of specs and some even show very small output.

I know that even Mark Levinson Dealers are using MJ15024/25 to replace 2N5686/64 as they are no longer available. That's why I make the choice to replace both units by matched pairs MJ15024/25.

Both units seems working very well after the replacement, but sounds pretty hash for the mean while. I think they need sometime to break-in.

My concern is whether I need to change the bias level. For using MJ15024/25.

Dennis
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Old 16th April 2006, 05:41 PM   #9
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Arrow Hot

Those bad sounding ML2s get normally too hot to touch.

:bs:
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Old 17th April 2006, 10:33 PM   #10
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Quote:
Originally posted by emergency
I know that even Mark Levinson Dealers are using MJ15024/25 to replace 2N5686/64 as they are no longer available.
It is still a current On-Semi device, and available through Digikey here...
Quote:
My concern is whether I need to change the bias level. For using MJ15024/25.

Dennis
I'd keep the same bias setting as the manufacturer recommends.
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