Transistors the 'wrong' way round?

[jaytee]

I read this on Wikipedia 'The bipolar junction transistor, unlike other transistors, is not a symmetrical device. This means that interchanging the collector and the emitter makes the transistor leave the forward active mode and start to operate in reverse mode. Because the transistor's internal structure is usually optimized to forward-mode operation, interchanging the collector and the emitter makes the values of α and β in reverse operation much smaller than those found in forward operation; often the α of the reverse mode is lower than 0.5'
The link here http://en.wikipedia.org/wiki/Bipolar_junction_transistor
Is it saying the hfe is much lower if you swap the collector and emitter? Is it ok to run a transistor like that?

[Meanderthal]

I've done it... if it gives you the sound you want, sure, it's ok. The OC140s can get really wierd that way- Ii have on e that has more gain backwards than forwards... And, I did tha t by accident for a BMP gain stage once, and kept it that way... liked the way it sounded.

[d95err]

Jack Orman has an article on this:

http://www.muzique.com/lab/reverse.htm

[R.G.]

The reverse hfe, which is also called "alpha" instead of the forward gain "beta" in the EE biz, is much lower - usually single digits and sometimes as low as 1/2, as the article said.

In this reverse mode, the withstanding voltage on the new "collector" (which used to be the emitter) is typically 5-7Vdc. Some transistors in reverse mode will work with a 9V battery for power, some won't.

It does not damage the transistor to run in reverse mode as long as you don't put destructive amounts of current through if it does break over.

Reverse operation is sometimes used for circuits where the transistor is used as a semiconductor switch, as the offset voltage is lower in this mode. But that was back in prehistory, before we had good JFETs and MOSFETs.

Some early germanium transistors were symmetrical, and worked about as well backwards as forwards. It depends on the exact doping of the collector versus emitter junction.