Re: TO3 & HEATSINK

From: exxos (exxos_at_home.co.uk)
Date: 07/28/04 

Date: Wed, 28 Jul 2004 20:59:38 +0100

"Norm Dresner" <ndrez@att.net> wrote in message
news:aWRNc.144975$OB3.12349@bgtnsc05-news.ops.worldnet.att.net...
> "exxos" <exxos@home.co.uk> wrote in message
> news:4107d861$0$6441$cc9e4d1f@news-text.dial.pipex.com...
> > > A little more expensive but good performance in the MJ150xx series of
> > power
> > > transformers. The complementary pair MJ15003/15004 are higher voltage
> > than
> > > you need but especially good for high power audio amplifiers. They're
> > still
> > > TO-3 but there's generally no real problem in routing wires through
the
> > heat
> > > sink if you protect them against rubbing and overheating by installing
a
> > > gromet in the hole. The 3055 is an old workhorse, best for low
> frequency
> > > designs like subwoofers.
> > >
> > > For TO-220 packages, consider a MOSFETs instead of bipolar output
> stage --
> > > there are some really good medium power units available in this
package.
> > > Norm
> >
> >
> > The MJ21194 power NPN looks nice, I have already tried some mosfets,
They
> > seem to sound the same, but when I look at set freqencys on the scope
the
> > wave is very much distorted, I've been trying this out for the past 2
> days,
> > ive tried everything I can think of, they just dont seem to work as good
> as
> > transistors do. I'm all for using mosfets, though I think for my next
> > project I'll design a class D amp and use some mosfets for that.
> >
> > Chris
> >
> >
> MOSFETs require different biasing and somewhat different drivers than
> BJTs -- you can't just substitute one for the other. There are a few
"good"
> books on the subject -- Doug Self and Randy Slone are the latest ones I've
> read.
>
> Norm
>

yeah I spent a while alterting the bias, the audio output sounded ok, though
somewhat lower volume, on sine wave test the sine on the falling edge seemed
to slow down as it came to the crossover point, I imagine the capacitance of
the fet isn't being discharged fast enough. I will look into those books,
should make interesting reading. whats the titles of the books ?

chris