500va transfomer 3 secondaries no centre tap

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Somebody correct me if I'm wrong, but for any given current, wouldn't doubling the capacitance in a half wave circuit give the same ripple (but different frequency) as a full wave circuit? (based on V=q/C where q would be the integral of the current over time) Another vote for big capacitors and beefed up diodes. Another 2 cents down the drain.

To a first approximation, yes. Just a little bit more is needed because the on-time of the diodes doesn't increase much while the period doubles so the off-time is slightly more than doubled. The capacitor ripple current is about a factor 1.5 times higher than the typically used non-doubler circuit so watch out for that too.

As long as the current draw is symmetrical there is no problem using this kind of circuit except the obvious drawback that it needs more smoothing capacity for the same ripple. If the current draw is nonsymmetrical however, a DC component will be drawn from the transformer which could push it into saturation due to the resistance of the primary winding. Full-wave doublers are routinely used in SMPS front ends in 120V mode even at multi-kilowatt levels if PFC isn't needed.

The current draw of an audio amplifier should be symmetrical over a sufficiently short time interval for a full-wave doubler circuit to be usable. That is, if you have enough space and money for the capacitors :D
 
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34+34 volts of AC obviously is not enough for 200W ... if this transformer has a bit of a gap between the coils an dthe case ...winding another 34 turns to make it a center tap might be possible ...or at least worth looking at it ...it might as well be

may you never make it to 200 W in a single mode but may be something brigged might do the trick or simply come closer to what you want ....

if you manage to proper 125W the diference from 200 is very very low
 
well using a SMPS as an example in favor of this scheme is not fair because
Older SMPS (non PFC) using full wave voltage doubler make no loading connection to the center of the cap string, so the ripple is 2x line rate, unlike audio amps that use the speaker return (load) directly to the center point. That is the main problem with using this.

Problem compared to what? Do you suggest that 50Hz ripple is worse than 100Hz ripple when valley, ripple RMS and pk-pk voltages are the same? The big drawback is that much more smoothing is needed - but if you can live with that then...

Symmetry is not guaranteed esp when the power amp is clipping!

Good catch. There could be asymmetric current draw if clipping asymmetric waveforms heavily. A typical DC protection circuit would be triggered though in such a case. The same "problem" exists if you use a single bridge symmetric PSU but use two separate transformers instead of a center-tapped/dual secondary one.
 
You could probably get that to do 200W into somewhere around 4-6 ohms bridged, but is it worth the trouble of making two amplifiers and needing double the power supply energy storage compared to a non-doubler circuit? :)

I'd get another transformer, like djk suggests.
 
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"properly designed transformers for tube amps using the full wave voltage doubler topology does not supper much from inadequate power delivery, this is a good place to look: powertranschokes"

So now he has to build a doubler and scare up a big power choke?

No thanks.

miscellaneous.html

115/220V Input Dual 41VRM 6.1A $20
(should be good for 200W/4R)

15-0042 93VCT 250Va $25.00
(should be good for 180W/8R)

Antek - AN-4450 $45 (new 50-0-50, should do 200W~250W/8R)
 
Sorry, been there, done that. Remove transformer frame, dis-assemble core, unwind primary of transformer, unwind secondary of transformer, determine the location for the center-tap, wind secondary, wind primary, re-assemble core, re-assemble frame, varnish.

My time is now more valuable than the cost of the proper part.
 
500va transformer

I still think i can do it with two bridge diodes set up and get my earth from them. I'll still get 43 volts + - I was thinking of hooking them up to the 34 vac secondary i believe it should work theres only one way to find out i was just hoping for a schematic to make life a bit easier. Thanks for the responses any more ideas or schematic would be appreciated :D
 
voltage doubler

I was definately wrong with that thought. I realised it was a quick way to blow a fuse! haha Oh well live and learn. Does anyone think i could push my luck with a full wave voltage doubler circuit i got the transformer for next to nothing and i really don't care if it blows up and iam using it for a band not music purist nice amplifier can anyone let me know how i can basically get away with doing it however just to get it running. Getting desperate. Hahah thanks
 
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