Hi to all,
I am trying to fix my NAD 7225PE stereo receiver and I need to replace the 2SB649AC (PNP) and 2SD669A (NPN) transistors.
I can't find these transistors at Mouser.
Can someone suggested a replacements?
I am trying to fix my NAD 7225PE stereo receiver and I need to replace the 2SB649AC (PNP) and 2SD669A (NPN) transistors.
I can't find these transistors at Mouser.
Can someone suggested a replacements?
Last edited:
Hi.
No wonder they cannot be found, they are obsolete.
Considering power rails i think MJE340/350 would do just fine.
No wonder they cannot be found, they are obsolete.
Considering power rails i think MJE340/350 would do just fine.
Hi yuria
2SB649AL and 2SD669AL are for sale at Profusion plc in England, they are cheap and of good quality, they sell abroad.
Good luck in fixing your Nad 7225PE
Best regards
rephil
MJE243/253
edit: Note that if the 649/669 blew, the outputs are probably bad too. If you replace the outputs, you need to add some 0.22 ohm 2W resistors into the emitter connections, or the outputs with thermally run away and blow again.
edit: Note that if the 649/669 blew, the outputs are probably bad too. If you replace the outputs, you need to add some 0.22 ohm 2W resistors into the emitter connections, or the outputs with thermally run away and blow again.
The maximum collector current are 0.5 A of your proposed transistors are less of the original which are 1.5 A.
Are you sure that 0.5 A currents are enough?
Do I need to add 0.22 ohm/2W resistors in series with the emitters of the main outputs transistors that's connects to the speakers?
Or to the series of the emitters of your suggested transistors?
To the main output transistors.
The reason is because power amps should always have some emitter resistance for some local feedback, which prevents thermal runaway issues, but NAD decided to skip it because they could "get away with it" for transistors that used the old hometaxial fabrication. Modern epitaxial devices WILL run away without some emitter resistance. This is a very common thing on these vintage NAD amps.
I would not use MJE340/350 as drivers. As you have correctly noted, they dont have much current handling.
Ideally, you would want better devices still. Unfortunately such parts are becoming hard to get. A closer fit would be Toshiba TTA004/TTC004, however I've personally found the MJE243/253 work quite well.
Far as T0126 the onsemi KSC3503, KSA1381 are pretty much the king now days
Since the vintage high Ft Toshibas are difficult to obtain
believe the 243/53 are about 40 mhz
and 100 volt, so depends on your rail voltage.
Your originals were 160 volt. So not sure what your amplifier requires
TTA/ TTC004 around 100 mhz
and the 2SC/KSC 3503 2SA/KSA1381
150 mhz
are closer to your original spec transistors 160mhz
MJE340/350 are junk slow general purpose
Since the vintage high Ft Toshibas are difficult to obtain
believe the 243/53 are about 40 mhz
and 100 volt, so depends on your rail voltage.
Your originals were 160 volt. So not sure what your amplifier requires
TTA/ TTC004 around 100 mhz
and the 2SC/KSC 3503 2SA/KSA1381
150 mhz
are closer to your original spec transistors 160mhz
MJE340/350 are junk slow general purpose
The 1381/3503 are not really drivers for BJT's - they are best used for MOSFETs or as VAS devices. The parts for the job were the KSC2690/KSA1220 however they are being EOL'd
The NAD is driving a single pair of quite slow devices, so the 243/253 work well. Their voltage ratings are plenty for this amplifier.
Profusion's 2SD669AL/2SB649AL versions suggested above by rephil, are manufactured by Unisonic in Taiwan and China. There are a number of reputable resellers of these and there are other Chinese producers with similar part numbers and similar to TO126 package, that appear to be compatible with the originals too. As said, the Hitachi/Renesas parts are long obsolete (I had difficulty buying them even 20 years ago) but the Unisonic parts are fine as replacements in the NAD amplifiers I've seen since then, such as this one. It's one of many types and variations of the NAD 3020 amplifier. There other manufacturers too - Wing Shing International comes to mind as another source or you can take your chances with the platform sellers on Ebay, AliExpress etc.