transistors like diodes

[devastator]

I saw a thread about that but I don't manage to find it again.

How use a transitor like diode ? all transistor can be used in diodes configuration ?

I'd like to try Ge transistor in a tube screamer gain stage.

[Greg]

You can use 2 diodes to make an npn tranny too!

Hmm

Have you done this.
Everything I've ever read says you can't.

A couple of quotes:-

"A transistor can be represented as two diodes, with a junction in the middle shown for both polarities in the figure above. This figure only shows an analogy for better understanding. Hence, connecting two discrete diodes in this manner as shown in the diagram will not make a transistor, because the point where they meet must be a common junction on the same piece of silicon (or germanium)"

"Remember, in the above drawing where I show a configuration of two diodes as being equivalent to the diode actions of a transistor, that this example is only for purposes of lead, and polarity identification. Two diodes a transistor doth not make! If you were to wire up two diodes in such a configuration you do not get any Beta gain at all, not even unity gain, what you get is a Beta gain of Zero."

[roseblood11]

One half of a transistor IS a diode...

Have a look at the thread about the zendrive, it uses a Mosfet in the clipping stage.

Or what Keeley calls his "5-star germanium mod":

Here is the tricky part of our mod, take a germanium (Ge) transistor and use the Base-Emitter junction (legs) of the device and use it in place of D6. If you use a PNP transistor, the Base will be the negative or cathode side, the Emitter will be the anode. Here is a diode drawing Cathode---|<----Anode. This increases the amount of distortion produced by the pedal, it also sound really nice. Try this! Don‘t leave it out! It‘s fun

(That´s from a SD-1 mod, works just the same for a Tubescreamer)

Immo

[Greg]

This is where I got the info from
But really,I was answering his question on using transistors for clipping
(this is what I imagine he was asking for)
Maybe you could help answer his question,and not just show where I was wrong?
That would be even more helpful

I don't see anything on that page that says you can make a transistor with 2 diodes ?

The point of my post was to correct wrong info so that people aren't mis-informed and confused...
I think that's very helpful.

[JiM]

Yep, a transistor contains two diodes. Two P-N junctions.
But two diodes don't make a transistor unless they are made on the same bit of monocristalline semiconducting material (Si, Ge, AsGa, InP ...)

To minimize the percentage of carriers that recombine before reaching the collector–base junction, the base region of the transistor must be made thin so that carriers can diffuse across it in much less time than the semiconductor's minority carrier lifetime. [...] The thin shared base and asymmetric collector–emitter doping is what differentiates a bipolar transistor from two separate and oppositely biased diodes that are connected in series.

[RnFR]

So are you saying ,if I use 2 silicon diodes,it will work as a tranny?
AMZ does good info for trannys for use as diodes for clipping

he's saying it won't work.

[devastator]

Oups I forgot answering to my own thread (I thought There was any answers)

Anyway, I tried to put two 2N5457 in a TS gain stage, and that works good (but I lose a lot of output volume). I connected the "drain" and the source (the gate is free). That gives a smoother sound, more satured too.

I didn't try Jfets in Hard clipping configuration.