What's important for transistors

[ray162534]

Hi, first post of newbie. There was a thread called smth like ''What matters and what doesn't'', that probably covers this, but can't find it.
I want to build an ampeg scrambler, but I can't get the necessary transistors [hate ordering via internet],. So what type of parameters should I compare when looking for a substitution. Srry for english and thanks

[R.G.]

It almost goes without saying, get the same type of transistor: bipolar junction transistor (BJT), junction FET (JFET), MOSFET, etc.

As a first consideration, transistor substitutions need enough voltage rating and current rating as the circuit needs. In 9V circuits, it's hard to find a transistor that will NOT work because the voltage is so low. Most transistors will do at least 20V. In small signal circuits like effects, currents are generally under 10-20ma, sometimes only uA. Those two ensure that the transistor will not die when put in to the circuit.

That leaves frequency response and gain. Frequency response is again one of those things where it's hard to get a device that will NOT work.

Gain is critical only in a very, very few circuits, notably the fuzz face.

The scrambler uses two darlingtons, as I remember, so get (a) small signal, (b) 20V or more, (c ) 10ma or more darlingtons in a single package.

It's up to you to find the pinout of the device that was supposed to go in the holes and match that to the device you actually get. Probably any small signal plastic package darlington device will work there. 

[ray162534]

Thanks for help