ESP Project 23

[tiroth]

For ESP Project 23 would MJE2955/3055 be appropriate input devices? I happen to have a lot of these lying around.

Thanks.

 

[paulb]

I think they would if the voltage ratings are okay (I haven't looked). I don't think you need much gain, which is good because the 2955/3055 don't have much.
If you really want to be sure, you can email Rod - he's pretty good at answering inquiries.

 

[lohk]

No, I think this is no good choice.
Power transistors rarely are good input transistors.

Why don't you make lots of good sounding amplifiers with this devices?

Klaus

 

[tiroth]

No, I think this is no good choice.

Really? This is not a circuit in the signal path, so "quality" is not really an issue as long as the circuit is still operational. Do you think it would not work correctly?

I should have mentioned that my rails are 42, so the max "normal" voltage the transistors should see is 39v, with a worst case (output shorted to unloaded rail) of 50v. I believe this is well within the 60v safe region. [output shorted to rail means I have bigger fish to fry, but I'd like to avoid secondary explosions in a fault state]

I would email Rod, but because he is so helpful to so many people I like to avoid bothering him where possible.

Thanks for your responses.

 

[lohk]

No, it is not a question of "quality".
MJE3055/2955s are designated output high current transistors, they need to be driven properly to function in an apropriate way. You can use them for input devices in sensing circuits for example, when high currents have to pass through. They have only low gain, and are quite non-linear at low currents, which can also be a problem here. And they are much bigger and more difficult to implement, and...
I think that they will not work the way you want. But if you insist, you can try it nevertheless ! It is up to you.
You can use - as Rod suggests - any transistor which meets the voltage specs. Current will be low, so possibly BC546/BC556 will work as an alternative. Boy, I have lots of these lying around ! (A zip-loc bag full of them actually...)

best wishes
Klaus

 

[tiroth]

Thanks for the suggestion lohk. I think I'll pick up some BC546/BC556 on my next order to be safe.