Transformer recommendation..

[Ian444]

Ooops, forgot about the center tap...

250V rectified would give 350V with no load, but under load, more like 320-325V. Then theres losses through the tube rectifier.

[Tdale]

that's withouth a center tap?

[Ian444]

250-0-250 or 0-250. It works out the same.

[Tdale]

Hmm..

I thought that 250 - 0 - 250 gave a theoretically output of 500V (two fases)....

Tommy

[Hellhammer]

Ooops, forgot about the center tap...

250V rectified would give 350V with no load, but under load, more like 320-325V. Then theres losses through the tube rectifier.

Yes I was only using it as an example, comparing centertapped and no centertap. 5V heater tube rectifier? Well that narrows it down further. So you need a 5V winding as well.

[Hellhammer]

250-0-250 or 0-250. It works out the same.

Well the current ratings differ.

If your 0-250 PT is rated for 100mA AC, you'd get ca 60mA DC out of it and that would be a lot for the PT, you wan't some reserve.

From a 100mA, 250-0-250 PT full wave rectified, you could get ca 100mA DC, but again you do want some reserve.

Hmm..

I thought that 250 - 0 - 250 gave a theoretically output of 500V (two fases)....
Tommy

It does but can be used for a 250V output as well. Read the Hammond design guide. It's all there.

[Ian444]

https://tubeamparchive.com/viewtopic.ph ... 916#100916

Tommy, there's some good reading here , look for the heading "The Power Supply", and have a look at these 2 topics - "Two-Phase, Full-Wave Rectifiers" and "Bridge Rectifiers". That will explain the voltages.

Hell, yes, lets just make it up as we go then, what do you reckon?

[Tdale]

But If I need a 250 - 0 - 250 transformer, a 0 - 250 won't do it.... The first has 500V between the leads, the other has 250V.....

Tommy

[Hellhammer]

Oh yeah and if you're using a valve recto you need the centertap or you could do a hybrid like this: [img:350:160]http://www.freewebs.com/valvewizard/Bridge3.jpg[/img]

[Hellhammer]

But If I need a 250 - 0 - 250 transformer, a 0 - 250 won't do it.... The first has 500V between the leads, the other has 250V.....

Tommy

Tommy! You're not reading the links we're posting!

You could use either. A 0-250 would need a higher current rating and a bridge rectifier though.

[Ian444]

+1