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

Nathan Trites nathan at idmclassics.net
Tue Mar 7 19:15:46 CET 2017


The dual transformer Rutger mention's is exactly what I've been looking for
lately and should work for us ... I need something with at least 2
secondaries that will go down to a 5v rail and a single 15v rail. I only
spent some time last night looking but I'm digging these Bel MT series
transformers that are designed for a 5v and +/-15 or 12v supplies.

this one is smaller, check the datasheet for more powerful options:
http://www.mouser.com/ProductDetail/Bel-Signal-Transformer/MT-6-15/?qs=0%2F2GmT7MRM%252bQI%252bgfp3ZvBQ%3D%3D

In our case we would only need to use half of the secondary with CT. If
anyone knows a source of similar transformers where theres no center tap
I'd love to see.

Best,

N

On Tue, Mar 7, 2017 at 7:27 AM, Rutger Vlek <rutgervlek at gmail.com> wrote:

> 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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