[AMRadio] Transformer help

[Bill Russell]

Hmmmm,
After reading all the stuff about swinging chokes in the past posts, I 
wonder why my Johnson Thunderbolt uses this type of choke. The amp is old 
as u all know and is designed for both AM and SSB as well as CW. If this 
choke is in deed not the way to go, I wonder if I should change it. I plan 
to add a bigger cap anyway so maybe I should change both the cap and the choke.

Bill KC2IFR




At 03:50 PM 2/16/02 -0800, you wrote:
>Part of the design criteria for a power supply is to make sure the
>inductance of the filtering network does not match a "critical" value, at
>which the filtering network approaches resonance.  Of course at resonance
>high voltages and currents are generated in the network, which is quite
>opposite of the intended effect from a power supply.
>
>A swinging choke's inductance varies with load.  The reason they are not
>used with SSB gear is because of the extreme current fluxuations with SSB
>driven amplifiers, especially when there is little modulation (no current
>draw).  At this point, the critical value of a supply using a swinging choke
>becomes very hard to avoid.  Swinging chokes work much better in a AM
>transmitter with a relatively constant current draw.
>
>73 de Bill, AB6MT
>billsmith at ispwest.com
>
>
>
>----- Original Message -----
>From: "Gary Schafer" <gschafer at mediaone.net>
>To: <amradio at mailman.qth.net>
>Sent: Saturday, February 16, 2002 2:56 PM
>Subject: Re: [AMRadio] Transformer help
>
>
> > Thanks Russ & Jim.
> >
> > That Is what I remember from long ago but now I am wondering if it would
>work ok
> > with a large filter cap like around 25 mf.  In the days when swinging
>chokes
> > were used a lot large values of capacitance were hard to come by.  I would
>not
> > be depending on the choke for any filtering, only voltage regulation.
> > Any thoughts ??
> >
> > 73
> > Gary  K4FMX
> >
> >
> > Tommye & Jim Wilhite wrote:
> >
> > > Russ is right about the swinging choke, Gary.  Good for AM, not good for
>ssb
> > > for the reason you cited.
> > >
> > > Jim
> > > de W5JPW
> > >
> > > >
> > > > Speaking of choke input, I wonder if a swinging choke only, will cause
> > > > problems on SSB. The supply that the transformer is going into has a
>20-4
> > > > henry swinging choke. It was used that way before but I am not sure it
>is
> > > a
> > > > good idea. I seem to remember from the early days that a swinging
>choke
> > > was
> > > > not recommended as power supply dynamic regulation would suffer badly
>?
> > >
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Bill Russell