Re: Happy St Patrick's Day, Boss!

In article <47E16BB3.25D484E6@[EMAIL PROTECTED]
>,
 Eeyore <rabbitsfriendsandrelations@[EMAIL PROTECTED]
> wrote:

> Iain Churches wrote:
> 
> > "Eeyore" <rabbitsfriendsandrelations@[EMAIL PROTECTED]
> wrote
> > >
> > > Designing with DISCRETE transistors is an art. The possibilities are
> > > endless. The real magic is of course the availability of npn and pnp
> > devices. Sadly
> > > there is no tube equivalent of a pnp.
> >
> > Graham.  Tube amps are delightful in their seeming simplicity.
> > I am always amazed how a 6SN7 triode and a handful of
> > components can play such sweet music:-)
> 
> That is of course one of their attractions and is similarly very
suitable for
> and attractive to the home constructor who can easily 'relate' to the
simple
> circuitry.
> 
> I don't know many people who can relate to an IC !
> 
> 
> > However, there are difficulties in tube amplifiers,
> > which I am told, one does not encounter in SS
> > amps as they do not have an OPT. Have you
> > ever tried to apply the optimum of NFB in a
> > tube amp while keeping a good stability margin
> > into say 0.22µF ?
> 
> Well .... since no normal speaker is represented meaningfully by a
0.22uF
> load, I'd probably not over worry about that.
> 
> Of course, one would first tend to 'isolate' that 0.22uF by means of a
small
> value output inductor in the case of the solid-state amp. In the case of
a
> tube amp, the leakage inductance of the OPT will do something broadly
similar.
> Of course, one then needs to be totally in control of the OPT design.

I thought that in a typical tube audio amplifier, with NFB taken from 
the speaker terminals, that the leakage inductance of the OPT increased 
the total phase ****ft, making the stability problem worse rather than 
helping?  For the leakage inductance to be helpful in the way you 
suggest I would think that the negative feedback would have to be taken 
from either the primary of the OPT, or from a special tertiary winding 
on the OPT.  Don't solid-state amps take the negative feedback from a 
point prior to the "output inductor"?


Regards,

John Byrns

-- 
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