SMPS for tubes - modification

[vasko]

I have a little amp with 2xPL84 in output and I want to make nice power supply for it

I decided to take functional 400W SMPS ATX power supply and to attach the secondary to my new transformer (primary) and then on that transformer to put the fast Gretz and to feed and heat lamps

original transformer in ATX I will not change it because it has feedback from 3.3V coil to the SC6105 to keep the voltage stable

So I need the following voltages:

160V and 200V for the anodes

9 and 15 V for heating pentode and triode

So I need information how many turns each winding should have for each voltage on my transformer?



I have a question whether the transformer in the ATX has a 1x12 or 2x12V on the secondary?

I've read on internet that 4 turns will give 12V.

Also what fast Gretz (or diodes) do you recommend to me?

[vasko]

no one?

[M1EUF]

The figure of 4 turns for 12V sounds reasonable, but it depends on the operating frequency, cross sectional area of the transformer and maximum flux density. If you dismantle the transformer or add a small test winding you will find this information out.
You will probably have difficulty rewinding the transformer because the primary will be wound in two parts with an equal number of turns, with the secondary windings interleaved between the two. To dismantle the transformer you will have to either bake it in the oven at about 150 degrees and pull it apart or soak it in NaOH or paint stripper which will take the enamel off the wire and ruin the insulation. It would probably be easier to design a new transformer from scratch.
'I have a question whether the transformer in the ATX has a 1x12 or 2x12V on the secondary?'
The secondary will be bi-phase (perhaps 4+4 turns for 12V with a double diode) if its a half bridge type converter (has 2 switching transistors) or a single rectifier if its a forward or flyback type (only has one switching transistor).
The rectifiers need to be ultrafast types, look up a datasheet for those fitted in the power supply, they may be suitable for your heater supplies. For the HT look for something like a UF5408 or similar.
I have been working on a simple self oscillating half bridge converter which would probably be suitable for your requirements, mostly using components from a computer smps. I will post a diagram when I get time.

[vasko]

it has 2 switching 13007 bipolar transistors, so its 2x12V on secondary I guess

something like this without these MOSFETs http://www.elitesecurity.org/t370885-2#2831938

or this http://www.goodbj.net/upload//080706152832021.gif

I have been working on a simple self oscillating half bridge converter which would probably be suitable for your requirements, mostly using components from a computer smps. I will post a diagram when I get time.

It can't have that stable voltage as with SC6205 with feedback

[M1EUF]

Originally Posted by vasko

it has 2 switching 13007 bipolar transistors, so its 2x12V on secondary I guess

something like this without these MOSFETs [es] - Napajanje ra?unara - drugi na?in

or this http://www.goodbj.net/upload//080706152832021.gif



It can't have that stable voltage as with SC6205 with feedback

But how stable does it need to be for a valve power supply? most valve circuits use a 6.3V and 250-0-250 transformer straight from the mains with no regulation. Perhaps your heater supplies could have a linear post regulator, but you may find that even if unregulated the output will be stable enough. It probably wont matter if the HT varies slightly, it depends on how stable your local mains voltage is. Mine is supposed to be 230 -10+15% but in practice its always 237.
How about taking the high frequency AC from the transformer before the rectifiers, and step this up with an external transformer? not very elegant but its simple and causes minimal disruption to the existing unit.

[M1EUF]

Originally Posted by M1EUF

How about taking the high frequency AC from the transformer before the rectifiers, and step this up with an external transformer? not very elegant but its simple and causes minimal disruption to the existing unit.

Sorry, just re-read your original post and realised that was your idea in the first place. I got carried away!

[vasko]

I have trouble to match the number of turns. I've put 4+4=8 on my primary and it seems that it's not enough because when I put 40W bulb load, protection turns on like I've put 400W load.

Here are the data:

ATX unloaded secundar 20V mesured rectified with 4xUF4007 and 300uF capacitator.
My transformer primary 8 turns.
On secondary 6 turns gives 6.7V loaded with tube filament (should be 9V).(voltage is higher but drops on 6.7V when loaded)
On secondary 10 turns gives 13V loaded with tube filament (should be 15V).
Also have 130 turns that I loaded with 40W bulb,said above.


I could use help about number of turns that should use?

[hesener]

On a flyback, putting a second transformer before the rectifier won't work. If you want to pursue this, try adding more turns if possible, and a voltage multiplier (using diodes and caps, like in a HV cascade) until you reach a sufficiently high voltage.
How about building a small (square wave) oscillator with e.g. 10V output, connect it to the secondary of a 12V/230V transformer (regular, off the shelf stuff), maybe with an inductor in series to damp the harmonics a little bit, and rectify the voltage from the primary (which now became the new secondary)?

just my two cents...

[vasko]

Originally Posted by hesener

On a flyback, putting a second transformer before the rectifier won't work.

You are the first one to say this. Can you explain it a bit?

[hesener]

In a flyback, the whole circuit basically depends on "storing" charge in the transformer in the first place (secondary side has no current), then turning off the primary switch at which point out voltage will have reversing polarity and the charge flows to the output. so it all only works when no current flows in the first phase,hence the use of a single rectifier (that is the reason why no bridge rectifiers are used in a flyback).
if doing that is your goal , you may want to look for a forward converter. These can easily be spotted because they must have an additional inductor after the transformer. Here, it should be possible to insert another transformer to obtain different voltages, although I never tried it (and haven't heard of anyone who has)... let us know if you tried it and it works ;-)