2sc1845 replacement

[hernanstafe]

I'm building quasi's amp and i can't get the transistor 2sc1845. I want to know if you can recommend any good replacements since i've been looking at some but they're not low noise, like the 2sc. Ideas?

[AndrewT]

Hi,
low noise devices in this postition will make little difference to the final output noise. Certain topologies will benefit slightly, the remainder will benefit even less from using low noise devices.

The way noise is defined in the datasheets is almost irrelvant to the way they are used in the front end of a power amplifier fed from a low source impedance.

The outcome of all this is to pick a high gain, fairly low Cob, sufficient Vce0 and fairly linear over the operating current range and some would add, fast enough to exceed the speed of most of the other devices further downstream.

[hernanstafe]

i was asking for a low noise device cause quasi told me so. Sadly, the only one i can get here is the 2n5551 but idk if it's good for what i want it

[AndrewT]

Hi,
the 5551 is a very poor substitute. Most of the preferred parameters are seriously compromised to achieve high Ic and high Vce0.
The minimum on most parameters are very low and one may find many devices that perform well in the majority but badly in just a few, due to these production spreads.

I suggest you look for hFE>400, Cob<6pF, Ic>50mA, Vce0>1.5*Vrail, Linearity < 1.25 over the range 0.5mA to 10mA, Ft>200MHz @ about 5 to 10mA,

[hernanstafe]

I've been all day looking for a replacement for 2sc1845 and i can't! any ideas please!

PS: Can i use darlington transistors instead of a common one?

[sklimek]

Originally posted by hernanstafe
I've been all day looking for a replacement for 2sc1845 and i can't! any ideas please!

Looks like Ebay has them at .40 a piece w/ a thousand available.

http://cgi.ebay.com/NEC-2SC1845-NPN-...QQcmdZViewItem

Here is the NEC data sheet:

http://www.datasheetcatalog.com/data.../2SC1845.shtml

Are there more than one manufacturer?

Stan