Re: OPT equalising circuit

In article <481F1CF4.4F319A91@[EMAIL PROTECTED]
>,
 Patrick Turner <info@[EMAIL PROTECTED]
> wrote:

> John Byrns wrote:
> > 
> > In article <d_BSj.6957$ko5.2719@[EMAIL PROTECTED]
>,
> >  "Alex" <apogosso@[EMAIL PROTECTED]
> wrote:
> > 
> > > Thanks, Partick.
> > >
> > > Your reply is constructive and informative, unlike the other one.
> > >
> > > My case is not a Hi-Fi amplifier, but a radio with a single-ended
stage. 
> > > OPT
> > > is quite lousy. It is designed for Rl=7.5K (for 6M5, EL80 or 6F6
tube at
> > > 250V). Its leakage inductance, referred to primary is as large as
165mH 
> > > --
> > > the windings are not interleaved.
> > 
> > There is an interesting variation on this capacitor thing that you
will
> > see in some old radios.  Rather than using a single capacitor which
> > slowly rolls off the high frequency response, two capacitors are used,
> > one across the primary, and another across the secondary of the output
> > transformer.  The two capacitors, along with the leakage inductance of
> > the transformer, form a third order low pass filter.  This provides a
> > sharp cutoff to attenuate noise energy above the desired audio band
> > while providing flatter frequency response below cutoff in the desired
> > audio band, than a single capacitor can.
> > 
> > Regards,
> > 
> > John Byrns
> 
> It was quite common to use caps from anode to the B+ so thus across a
> driving triode's load
> and the OPT primary, and indeed there is a 3rd order LPF.

How do you get a 3rd order filter out of this, it looks like a 2nd order 
filter to me?


Regards,

John Byrns

-- 
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