help with transformer

[jarthel]

I am looking at 2 transformers and these are the specs

xformer1:
S1: 60V-240V-260V
S2: S3: 2.5V-0-6.3V


xformer2:
S1: 280V-0-280V
S2: S3: 2.5V-0-6.3V
S3: 5V-6.3V

I'm not really an expert with these things but with xformer2, do I have 560V to play with?

what about xformer1?

All I need is a xformer that can feed a rectifier tube that will then be filtered by caps, chokes and resistors to give me a final output of around 250V to be used on an Aikido 9pin pcb.

Thanks for the help.

[AndrewT]

Hi,
the second would allow you to use your tube to rectify each half of the 0-280 output.
I do not know the losses through the tube but I would expect a lot more than 300Vdc output. Can you lose all this voltage in the following filter?

The first will require a bridge to get your DC. I think this is less common on tube rectification.
If you went with SS bridge then the output will still be high with the 240Vac tapping. But the 200Vac (260-60) tapping might be about right.
Can you tube rectify the single 0 to 240Vac tapping?

[jarthel]

Originally posted by AndrewT
Hi,
the second would allow you to use your tube to rectify each half of the 0-280 output.

I will be using a full-wave rectifier. It would either be a Bendix 5852 or a 5U4G/5V4G. Does that mean the tube will connected to the 280 wires? Thus I have 560VAC?
=================
I'm playing with PSU designer right now and a 560VAC on a 5V4G gives out around 600+V on the 1st cap.

but a 200VAC on an CRCLC config, the voltage across the 1st cap is 259V.

Does this means that the 1st xformer is suitable for my use?


==========

unrelated question to the original topic:


the secondary for the 2nd xformer: can someone explain how can I get a 6.3V on it? I'm asking as there is no "0 tap" like the 1st xformer.

Thank you very much for the help

[AndrewT]

Hi,
your tube is effectively two diodes.
Each half of the transformer goes through just one diode. So the tube rectifies half the centre tapped secondary on each half mains cycle.
So you get 300V or a bit more from the 280Vac.

A SS rectifier will give you 395Vdc from the 280Vac. I think the tube will lose 20V to 40V compared to 1.4V so I would expect an output of 350Vdc or a bit over from 280Vac CT secondaries.

Your second example showing 259Vdc from 200Vac makes more sense of the root2 times Vac less losses.

Could the 0V wire have broken off? Is there a 0V wire on transformer 1 for the 60,240,260 taps?