BF871 and bf872 equivalent?

[sam18]

my package liabry doesn't have these two transistors. does anyone know any equivalents?

 

[homemodder]

Bf471,BF472 will be good replacement. However its not easy finding these transistors anymore. What is the purpose of the transistors ??

 

[sam18]

its for apex's 150w mosfet amp
http://www.diyaudio.com/forums/solid-state/163159-150w-mosfet-amplifier-irfp250x2.html

 

[homemodder]

The bf471 would do or you could try find 2sc3503 or 2sc2911. Its also a matter of where you want to purchase the parts from. If you can wait few days you could purchase via internet. In this case youd be able to find most of those bf parts at Nikko electronics in Surrey.

 

[reji]

hi guys, im also looking for equivalent for BF871 for the same MOSFET amp.anyone knows that MPSA42 is substitute for BF871.i want to make the this circuit in SMD version.

 

[MarianB]

Why not go with the more common MJE340/350 pair?

 

[homemodder]

Because it has poor performance compaired to the ones mentioned in this thread.

 

[homemodder]

hi guys, im also looking for equivalent for BF871 for the same MOSFET amp.anyone knows that MPSA42 is substitute for BF871.i want to make the this circuit in SMD version.

No its not, what about SOA. What is the current through those transistors ??

 

[MarianB]

Because it has poor performance compaired to the ones mentioned in this thread.

Of what poor performance you are talking about?

 

[homemodder]

High Cob, will cause high, high frequency distortion. The mje340 have at least 25 pf wheres the others dicussed sit around a max of 3pf at 10v vce.

 

[homemodder]

For SMD one could use bf721, excellent transistor, but watch not to stress the SOA as these too cannot handle as much power as the TO220 or TO126 packages.

 

[Bonsai]

I agree- MJ340/350 are not a good choice for the VAS. I used KSC3503 and KSA1381 from Fairchild and they work well. Cob is low which is important for VAS/TIS applications.

On my previous power amp I used BF471 and BF472 and had no problems, although they are driving an EF3, so the loading is quite light. Be warned, the models for these BF devices are very problematic for some reason. And, Philips (NXP) discontinued them quite a few years ago.

 

[reji]

is there any MPSA series is equivalent for BF871?

 

[reji]

MPSA92 is a substitute for BF871?

 

[reji]

MPSA92 is a substitute for BF871?

 

[jacco vermeulen]

Of course not.

You need something in a TO126 package that does 300Vce, e.g. Sanyo video transistors, C3502 and up.

 

[Samuel Jayaraj]

I use 2SA1538/2SC3953. Very low Cob and great performance. May also be easier to find, although the PNP is harder to find than the NPN one.

 

[MarianB]

Please excuse the apearent ignorance but i have just consulted 6 different datasheet's for the MJE340 transistor and i didn't find any refference of COB for that transistor, so where did you took those figures from?

On the other hand, most of the transistors you so call best for the VAS have verry small IC so what if it must drive an BJT power output stage with more than 4 or 5 otput pair devices? no matter what buffer you will use it will still load the VAS on it's upper limmits. I think if enough current is given than that capacitance is of no consequence, the audio upper limmit is around 20Khz, and a good desighn of the VAS will push any distorsion above that, so if you cannot hear any, why bother fixing it?

 

[Ian Finch]

Cob is one problem of MJE340/50 used as VAS. Ft is not so good either. The general picture is that they are too slow for a good VAS in any high rail amplifier where you expect high quality, low distortion audio. If you draw more than a few milliamps from any VAS transistor you will be rewarded with more distortion than is possible by buffering. Where multiple (BJT) devices are used, it always makes sense to use a triple output stage and thus there is no real problem with even tiny VAS currents.

That is exactly the reason for using these video driver transistors - they make the best quality BJT VAS devices available for the money.

 

[MarianB]

That is not what i asked, i already knew why BF's are prefered, what i asked is where do you get the Cob caracteristic for MJE340, since in the datasheet is not listed, but nevermind...