Re: OPT equalising circuit

"John Byrns" <byrnsj@[EMAIL PROTECTED]
> wrote in message
news:byrnsj-FE9DF8.20272704052008@[EMAIL PROTECTED]
> 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.

I have never seen that, but it is an interesting idea. Might be useful on
SW. Requires a set of switches to throw relatively large caps in circuit.
As
I understand, you need to turn the feedback off  for this 3-rd order
filter
to have effect. Turn the NFB off and the mechanical resonance of  the
speaker will be undamped. So, there needs to be a special circuit,
gradually
disabling the feedback with the frequency rising, but not affecting gain.
It
can be done. And what if we place more LC pads between the secondary and
the
speaker? Potentially can make the radio fit to receive SSB...

>
> Regards,
>
> John Byrns
>
> --
> Surf my web pages at,  http://fmamradios.com/