F!shman LoudbOx MOSFET blown, transistor substitution help, please!

Hi you all,

first post of 2009, HAPPY YEAR to you all

I blew the output of my F!shman Loudb0x.

I am looking for equivalents for the 2n5551/ 2n5401 MOSFET drivers.
these are rated 160V/Ic =500ma
I was thinking of the BC640/639 combo as it's 80V(ok as +/-33V supply in my case), 1A max

Have a look at the schematics attached!

I guess it's ok but, I prefer being reassured

thanks

Maxime

Probably o.k.

One remark:  one of the reasons you see the 5401/5551 combo used in audio circuits, even when the breakdown voltage is not necessarily needed, is the constancy of beta with collector current.  This was likely an unexpected consequence of the design for high breakdown voltage.

But the curves on the Fairchild datasheet for the BC640 look pretty close to the Toshiba curves for the other parts, and the circuit has lots of local feedback, so I doubt there is much of a concern.

thanks a lot for the reply, bcarso!

I'll keep you informed

best

maxime

It works great,

I tested the 2n5551 they were all ok,
but the 2n3904, earlier in the chain, was blown. I guess it's what blew the mosfets.
it was not heatsinked in a proper way.


thanks

best

maxime