Huge hfe's

[magikker]

I came into the possession of three transistors I've never worked with before. Long story short someone thought I might be able to make something useful out of them. I've made a couple effects but I'm still in the follow the schematic phase of building.

Do you guys know if a NTE47 is worth anything when it comes to pedal building?
The back of the box lists it as hfe 1150 typ which seems awfully high.
http://www.nteinc.com/specs/10to99/pdf/nte47.pdf

[Paul Marossy]

That does sound high. Probably too high for use in a stompbox because it would most likely be noisy, especially if they are not specifically designed for audio use like a 2N5089 or similar transistor.

[Paul Perry (Frostwave)]

Well it's only 3 times as high as the average modern silicon transistor, so whether it is OK in any given design depends - as always - on the design itself.
Note that in a simple one transistor amp, the gain is set either by negative feedback through an unbypassed emitter resistor, or by the choice of collector resistor.

The only downside is, sometimes you find high gain transistors acting as 200MHz transmitters, particularly if the layout is a bit random.

I've had transistors here that put my DMM HFe off the scale (that is, more than 3 digits) and they worked fine in stuff.

[magikker]

Well in some good news for me, I found out they are similar to MPSA18's which are used in the tripple fuzz that I want build.

[ambulancevoice]

you think thats a big hfe?
the mpsa13's at my local store are 5000
and the mpsa14's at another are 10000 (im not sure if thats true though)

[Seljer]

you think thats a big hfe?
the mpsa13's at my local store are 5000
and the mpsa14's at another are 10000 (im not sure if thats true though)

those are darlington pairs http://en.wikipedia.org/wiki/Darlington_transistor
the total hfe is the product of each transistors individual hfe so its very easy to get huge gains

[ambulancevoice]

yeah, i know what a darlington is, obviously, how could i not?
and how you can make your own with two transistors hooked up emitter to base and collector to collector (with the second emitter to ground, or whatnot)
i was just saying anyway
thats still unsual hfe though

[magikker]

Well I could put two of mine in a pair and see what happens.

[Paul Marossy]

As Paul Perry says, it depends on the circuit design. They may not work well in really high gain circuits because they will amplify the hell out of any circuit noise. 

[magikker]

True, true,  But lucky for me they have the words "lo noise" written on the box.