[sdiy] replacing a transformer, was:Re: (no subject)

Rutger Vlek rutgervlek at gmail.com
Tue Mar 7 13:27:07 CET 2017


Good point Ingo!

Towards the end of the service manual (
http://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Yamaha-A-3-Service-Manual.pdf)
the PSU schematic is displayed. There's a full PSU diagram, and an overview
diagram. The latter shows a straight coupling between both DC grounds of
the 12V and 6V lines, however the first diagram does not! Confusing, I'll
measure this in the actual unit to be sure.

Assuming both grounds are connected, what you wrote is applicable here. So
it means I'll have to start looking for a transformer with dual independent
secondaries for 6.3V and 13V (or 12.6V). Anyone knows one? At least 7VA
total.

Regards,

Rutger


On Mon, Mar 6, 2017 at 6:06 PM, Ingo Debus <igg.debus at gmail.com> wrote:

>
> > Am 06.03.2017 um 14:00 schrieb Roman Sowa <modular at go2.pl>:
> >
> >>
> >> Is there any harm in using the centre tap for the 6.3V and the end taps
> >> for the 12.6V supply to the PSU? It means the coil between one end and
> >> centre tap gets a little more loading than the other side. The same
> >
> > No problem at all, just make sure that added load from 6V and 12V
> circuits doesn't exceed current rating for that winding.
>
> Careful. This won’t work if the two secondary windings of the original
> transformer are isolated from each other, and they are feeding two bridge
> rectifiers, and on the DC side of the bridge rectifiers the grounds are
> connected.
>
> With two half-wave rectifiers there’ll be no problem however.
>
> Ingo
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