[Boatanchors] Lowering Receiver B+, Again.

[Gary Schafer]

A full wave bridge on 1/2 of the transformer will give you the same voltage
as the full wave rectifier using the full transformer. It will also overheat
that 1/2 half winding as the power load will all be there rather than split
on the full transformer.

Someone suggested using a 1/2 wave rectifier on 1/2 the transformer. That
will also give you the same voltage as the full wave rectifier using the
full transformer but with 2X the ripple.

The best method is to use the choke input with the full wave rectifier as
Rob suggested.

Getting rid of the 80 tube and replacing with solid state rectifiers and
some series resistors is a good idea to save the filament current.

If you do use solid state rectifiers with a choke input be sure to put a
small capacitor, such as a .01 mfd on the input side of the choke to kill
the noise generated by the diodes.
I had a choke input supply in a home brew receiver and I chased the noise
for years until I put the small capacitor at the input. Completely got rid
of the diode hash. 

(note: I only hauled out the project every year or so to do updates on it
until I got tired of it then it went back on the shelf for another year or
so.)

73
Gary  K4FMX

> -----Original Message-----
> From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf
> Of Bob Groh
> Sent: Thursday, December 22, 2016 8:34 PM
> To: Rob Atkinson
> Cc: Boat Anchors List; David Stinson
> Subject: Re: [Boatanchors] Lowering Receiver B+, Again.
> 
> Hummmm.  These are a few, somewhat off the cuff comments on the subject:
> 
> First, I would use a bucking transformer - probably 12V or so.  This
> will
> have the benefit of dropping the voltages - all of them including the
> filaments.
> 
> Second I would replace your rectifier with a solid state bridge - but -
> I
> would drive it only off 1/2 of the secondary HV winding. This would
> reduce
> the HV by about 1/2 or there abouts. Got to think a bit more about that
> -
> unfortunately I would really like a solution that takes some current
> from
> each side of the CT.  But somehow got to get a solid state rectifier in
> there - saves a bunch of filament power (5V at 2A or so).
> At any rate, not a complete solution but I'll give it some more thought.
> Certainly ties in with my work with restoring old receivers. More later.
> 
> 73
> bob Groh, WA2CKY
> 
> On Thu, Dec 22, 2016 at 10:44 AM, Rob Atkinson <ranchorobbo at gmail.com>
> wrote:
> 
> > get a small 5 to 10 Hy choke and convert it to choke input supply.
> > make sure it can handle the current demand.
> >
> > 73
> >
> > Rob
> > K5UJ
> >
> >
> > >
> > > As originally designed, the output of the full-wave
> > > B+ rectifier (type 80 tube) at the capacitor-input
> > > filter is a needless 340V
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