Cross reference

[Dr.EM]

I have often made this circuit with 2N3906 as they were convenient:

http://www.mp3forkidz.com/mic/phantxy.html

But they arn't the quietest transistors. I tried to find an equivalent to the NTE159 ones specified on the diagram. I used this site:

http://www.cedmagic.com/tech-info/rca-diode-transistor.html (near the bottom, the NTE number is a link/in blue)

The cross reference was found as PN2907. Thats good, my electronics supplier stocks them, but on the datasheet I cannot find a noise figure (the critical aspect here). Can it be assumed to be the same as the NTE159 (is it indeed the same part)?

Another (I think) suitable one I've found is the BC560. This appears to be a low noise model with high enough voltage rating for the circuit. It isn't as readily available to me though (only at Maplin, limited stock locally).

 

[Nigel Goodwin]

I would suggest an NTE159 is the equivilent of a BC159, a PNP version of the low noise BC109.

 

[Dr.EM]

Thanks, thats interesting. I would have thought it would be common since the BC109 is, but when I look for its datasheet, the best I can get is some old foriegn (Spanish?) one . Neither Maplin or Rapid have them. Is it very old or something?

I'm thinking the BC560 is better than the PN2907 for this application, but still haven't found the PN2907 noise figure

 

[audioguru]

The BC109 was an NPN in an old metal case. The BC179 was its PNP version.
The BC149 was an NPN in an odd-shaped plastic case. The BC159 was its PNP version.
I think they are all obsolete.

The BC549 is an NPN in a modern TO-92 plastic case. The BC559 is the PNP version.

They were, are all low noise. I still have some of all of them!

 

[Dr.EM]

Interesting. I can get the BC179, it has a good noise figure but is low voltage (only 20v apparently), I need one 40v+. This is what rules out the BC559 too, which I have a few of. The BC560 appears to be a higher voltage model of it though? I can get it here for quite a high price and depending if its in stock locally (don't want to pay for delivery whereas I'd get it free at Rapid by buying along with other parts):

**broken link removed**

It just says BC560, I think BC560C is best for low noise? Either way, the BC560 seems to show under 4db, typ 1db which should be fine. Anyone know how that PN2907 compares on noise? Or the BC636?