Luxman m4000 transistors

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vyju

Member
Joined 2004
Hi,

My Luxman M4000 power amp suddenly started acting up last week.

It was working fine but suddenly the left channel cutoff. On switching off and
powering it on again both channels worked but the left channel cut off after a
few seconds.

I took the amp to a service tech. who traced the fault to the front end
transistors.(first differential amplifiers)

The transistors are 2SA810. Part number Q301 and Q302 as per the M4000
service manual.

I require four of these transistors.(I will change the ones in the right channel
also.)

Please tell me a source for these transistors.

Regards
Rajiv
 
djk

djk

R.I.P
Joined 2001
The diff pair only need withstand the one rail voltage, not the P-P.

The Vas must withstand the P-P.

The Luxman M4000 suffers from poor solder joints and speaker relay issues as well. I would check for these issues before replacing the diff pairs (unless they actually measure defective).
 
V

vyju

Member
Joined 2004
Hi,

Thanks for all the inputs.

That is probably not the problem in this amplifier, unless one of them has actually failed.
Click to expand...

The transistors from the working channel were swaped into the defective channel and the channel started working.

When the transistors from the defective channel were put into the working channel it stopped working.

Regards
Rajiv
 
V

vyju

Member
Joined 2004
Hi,

I have ordered some 2N5401 transistors for the M4000.

The specs for the 2SA810 show the Maximum collector power dissipation (Pc): 700mW

The specs for the 2N5401 show the maximum collector power dissipation as 310mW.

Will there be a problem using the 2N5401 in the Luxman M4000?

Regards
Rajiv
 
E

ej25awd

Member
Joined 2007
sites.google.com/site/ej25awd/home
Amplifier designers put margin into their design that takes into account when the amp is working and NOT working (i.e., an open resistor/track/solder joint that will expose one stage to higher than normal voltage). There's a reason why a 150V part was chosen.

djk said:
The diff pair only need withstand the one rail voltage, not the P-P.
.
Click to expand...
 
Ian Finch

Ian Finch

Member
Joined 2010
Paid Member
On the choice of input transistors(and there are more good ones), a low noise figure like the
2SA970/2SC2240 complements is a better choice than 2N5401/2NSSS1.Just beware they are
obsolete and fakes will be around. For the cost difference, you may as well do the best you
can if you want the effort to be worthwhile. Check this spreadsheet
http://www.diyaudio.com/forums/soli...ata-sorting.html?highlight=transistor+sorting
 
Last edited:
Ian Finch

Ian Finch

Member
Joined 2010
Paid Member
See above spreadsheet for Fairchild KS types and salient details. KSA 992/C1845 have proven good from resellers or direct - which is how I buy.
I should have been specific, as last I looked, Toshiba had not deleted but they were on final production status or such and had been for ages, so assumed by now obsolete. The stock position is interesting; there is a lot about everywhere on Ebay and cheap. A friend bought 100BL "pairs" and got 200 rubbish and another bought through RS from UK stock, and got something bad for noise figure too. Otherwise, they seem OK here at E14, Mouser &, Digi-key but I would no longer use them if the part wasn't mandatory.
We might wonder how fakers would profit from low cost TO92 parts.
 
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