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Old 21st November 2002, 10:35 AM   #1
Hamish is offline Hamish  Australia
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Default NEC transistor equivalents, for old NAD amp

at the moment i am TRYING to repair an NAD 3045 intergrated. i am trying to find replacement part numbers for the transistors on the heatsink. 2SB539, D287B (both TO-3cases)and a small TO-126 which has the markings P827 90139. These transistors are on the left channel (which is working fine), but replacements on the right channel are MJ2955 and 2N3055. are these correct? the TO-126 on the right case is marked C2690A. is this correct also?
(the original transistors are NEC)
please, please help me!

much thanks if you can,
Hamish

i am new to this forum, but it seems like a much friendlier place than others. (more helpful too, i hope!)

keep up the good work
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Old 21st November 2002, 11:13 AM   #2
halojoy is offline halojoy  Sweden
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Guess it is a VERY old NAD. NAD 3020 was one old classic.
But surely transistor replacements are to be find.

Are you going to replace the Electrolytic Capacitors?
It is a good idea on old Amplifiers.
The (volume)-potentiometers and switches can also need a replace.
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Old 21st November 2002, 11:14 AM   #3
UrSv is offline UrSv  Sweden
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Is it 3045 and not 304?

/UrSv
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Old 21st November 2002, 11:24 AM   #4
Hamish is offline Hamish  Australia
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Default answering both at once...

yes, it is a 3045 (old, old, OLD). Electrolytic caps will be replaced soon (i am a student, so good quality 10,000uF caps are wish-list items). All pots and switches will eventually be changed.

if you guys can help, the left channel works fine, but the right channel has a LOUD low frequency noise (even when the volume is right down). it keeps frying resistors in the right channel also. could this be the amp or pre-amp section? i am new to all this, so don't be to technical.

thanks for the replies. it's nice to know that you can get help from around the world!

Hamish
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Old 21st November 2002, 11:43 AM   #5
Vigier is offline Vigier  Netherlands
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Hi,

2SD287 = Silicium-N-Channel, 200V, 10A, 100W, 8 Mhz
2SB539 = Silicium-P-Channel, 130V, 10A, 100W, 7.5 Mhz

Click the image to open in full size.

Not REALLY complementary, but OK, let's get the 2955/3055 info:
The MJ2955 and 2N3055 ARE complementary (so don't look at the prefix), and the spec's are: 100V, 15A, 115W, GBW=2,5 Mhz minimum.

If your DC-voltage isn't TOO high (smaller than 50V symmetric), then there will be no problems.
The GBW is not really a problem, since 2,5 is absolutely high enough.

Grtz, Joris

P.S. 1: C2690A = 2SC2690A in case you didn't know
P.S. 2: Do you have a suffix for the 2SB539
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Old 21st November 2002, 11:49 AM   #6
Hamish is offline Hamish  Australia
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suffix for the 2sb539 is r53
suffix for the d287b is r79a.

i hope this is right! there is no other lettering on the case (photo looks same except for lower codes)
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Old 21st November 2002, 12:25 PM   #7
Vigier is offline Vigier  Netherlands
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Heej,

no, that's a date-code, I hoped for a A, B or C suffix, but well, it's not THAT important.

I don't have the schematic of the amplfier, but I can tell you that the 2SB/2SD transistors are MUCH better than the MJ/2N set. (2SB and 2SD were specially made for audio, while ev'rybody thinks the 2SA/2SC were... MJ and 2N are definitely NOT).

What you could do is replace the Base-resistor with another one with a higher value (what resistor "lighten's up"???)..
That should help a lot. Another possibility: If the amp has emitter-resistors, you can replace them with a higher value (for example from 0.10 Ohm to 0.15 Ohm (MARK THE DISSIPATION!)

The last idea I have is the bias-current setting. Maybe the current is too low for these transistors. If you can measure it, it's an idea to set it at at least 50mA (if it's lower at this moment). If you replace the transistors, you always have to re-measure the bias-current and reset it.

Those were the first things that fell into my mind...

Grtz, Joris

P.S. Please don't comment my english... I'm a Dutch Kaaskop
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Old 21st November 2002, 01:22 PM   #8
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Quote:
Originally posted by Vigier
Heej,
[snip]
The last idea I have is the bias-current setting. Maybe the current is too low for these transistors. If you can measure it, it's an idea to set it at at least 50mA (if it's lower at this moment). If you replace the transistors, you always have to re-measure the bias-current and reset it.

Those were the first things that fell into my mind...

Grtz, Joris

P.S. Please don't comment my english... I'm a Dutch Kaaskop
Since he reported frying the resistors and a loud low freq noise, it may be that the bias is too high (noise could be the transformer straining to keep up the good work. do these things have separate xformers?).

Jan Didden (another Kaaskop)
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Old 21st November 2002, 01:26 PM   #9
Vigier is offline Vigier  Netherlands
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Good idea Jan,

replace the base-resistors of the MJ/2N pair with higher values, and reset the bias-current (try 50mA).

But, if your bias-current is TOO high, probably your heatsink is VERY hot!

Grtz, Joris
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Old 21st November 2002, 01:27 PM   #10
halojoy is offline halojoy  Sweden
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I wonder if the low freq, can be due to ALL dried out Big Electrolyts in the power supply.
But could that lead to frying?
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