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Paul D. Spiegel Paul D. Spiegel is offline
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Default Bridge or Center Tap?

For my next project I have acquired a transformer with two identical 450v
secondary windings. I could put the windings in parallel and use a bridge
rectifier. Or, I could put the windings in series and ground the coupling
for a 450-0-450 configuration to use with a pair of diodes.

Which would you do? What are the pro's and con's of the two
configuration?

For this project I am using SS rectifiers. Were I using a tube rectifier
I would go with the center tap, of course.

- Paul
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flipper flipper is offline
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Default Bridge or Center Tap?

On Thu, 20 Sep 2012 22:36:11 -0700 (PDT), "Paul D. Spiegel"
wrote:

For my next project I have acquired a transformer with two identical 450v
secondary windings. I could put the windings in parallel and use a bridge
rectifier. Or, I could put the windings in series and ground the coupling
for a 450-0-450 configuration to use with a pair of diodes.

Which would you do? What are the pro's and con's of the two
configuration?

For this project I am using SS rectifiers. Were I using a tube rectifier
I would go with the center tap, of course.

- Paul


A bridge is a little more efficient, say 20%, on transformer loading
than full wave center tap so if the VA is tight use a bridge.
Otherwise you can 'save the cost' of two extra diodes, which doesn't
count for squat in solid state but did with tube rectifiers.
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GRe GRe is offline
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Default Bridge or Center Tap?


"Paul D. Spiegel" wrote in message
...
For my next project I have acquired a transformer with two identical 450v
secondary windings. I could put the windings in parallel and use a bridge
rectifier. Or, I could put the windings in series and ground the coupling
for a 450-0-450 configuration to use with a pair of diodes.

Which would you do? What are the pro's and con's of the two
configuration?


Pro bridge/windings parallel:
- Better B+ regulation because HV-winding resistance is halved.
- Less heat development in HV-winding.
- Diode reverse voltage stress about 635V versus 1270V for the center tap
config.

But... are you sure both HV-winding voltages are exactly identical?
Otherwise one winding is supplying current to the other one by
voltage-difference/2*winding-resistance.

Con bridge/windings parallel:
- 4 diodes needed in stead of 2 for a center tap config.

Rgds,
Gio



For this project I am using SS rectifiers. Were I using a tube rectifier
I would go with the center tap, of course.

- Paul





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Phil Allison[_3_] Phil Allison[_3_] is offline
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Default Bridge or Center Tap?


"Paul D. Spiegel

For my next project I have acquired a transformer with two identical 450v
secondary windings.



** You ought to check that by connecting the windings in series and reverse
phase.

Then measure the voltage across the ends - it needs to be no more than 0.1
volts.

If all is OK, parallel connection is possible and preferable.



..... Phil


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John L Stewart John L Stewart is offline
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Quote:
Originally Posted by Paul D. Spiegel View Post
For my next project I have acquired a transformer with two identical 450v
secondary windings. I could put the windings in parallel and use a bridge
rectifier. Or, I could put the windings in series and ground the coupling
for a 450-0-450 configuration to use with a pair of diodes.

Which would you do? What are the pro's and con's of the two
configuration?

For this project I am using SS rectifiers. Were I using a tube rectifier
I would go with the center tap, of course.

- Paul
Hey Paul, I think I may have corresponded with you a few years ago with regard to my take on Crowhurst's Twin Coupled Amp. Was that you?

Anyway, here is my take on the FWB as opposed to the FWCT systems. An important consideration for PS designers is something called 'Utility Factor' of the various windings on the PT. Others have already noted the FWB to be better if that connexion is possible. I've attched a numerical example here for the secondary winding UF for the FWB with cap input filter. Since there are no other windings the primary & secondary UF's are equal.

Other examples will follow but in following posts since file size is limited here in AudioBanter. But in summary the best UF for single phase work is the FWB with choke input to fillter. The lost power during the conversion from AC to DC is in the form of the even order harmonics (2nd, 4th, 6th...Etc) generated by the rectifying process.

You could check for the possiblity of circulating currents in the parallel connexion of your PT secondaries as follows. Connect one end of the secondaries in series opposition. Then with an AC VM check for any voltage differance.

My guess is the voltages are near equal but with somewhat different resistance, all OK to parallel permanently. Sounds like you have a PT built from the core up to be series or paralleled, commonly available. For example, Hammond lists many such devices.

Cheers to all, John
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John L Stewart John L Stewart is offline
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Quote:
Originally Posted by Paul D. Spiegel View Post
For my next project I have acquired a transformer with two identical 450v
secondary windings. I could put the windings in parallel and use a bridge
rectifier. Or, I could put the windings in series and ground the coupling
for a 450-0-450 configuration to use with a pair of diodes.

Which would you do? What are the pro's and con's of the two
configuration?

For this project I am using SS rectifiers. Were I using a tube rectifier
I would go with the center tap, of course.

- Paul
Here is a similar circuit but this time with choke input to filter. You can see the SUF (& PUF) have gone from 0.586 to 0.883. All these numbers are ideal & the best possible. There will be other losses in all, but this gives one an idea of what is possible. Some 3-phase circuits are quite a bit better, another reason 3-phase is in common use for any large power requirement.
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John L Stewart John L Stewart is offline
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Quote:
Originally Posted by John L Stewart View Post
Here is a similar circuit but this time with choke input to filter. You can see the SUF (& PUF) have gone from 0.586 to 0.883. All these numbers are ideal & the best possible. There will be other losses in all, but this gives one an idea of what is possible. Some 3-phase circuits are quite a bit better, another reason 3-phase is in common use for any large power requirement.
Guess I hit the send key on that one too soon. I will blame it on old age. Better get on the bicycle again!

The bottom line as far as UF is concerned is shown in the lower RH corner of each of the examples.

Cheers, John
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John L Stewart John L Stewart is offline
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Quote:
Originally Posted by Paul D. Spiegel View Post
For my next project I have acquired a transformer with two identical 450v
secondary windings. I could put the windings in parallel and use a bridge
rectifier. Or, I could put the windings in series and ground the coupling
for a 450-0-450 configuration to use with a pair of diodes.

Which would you do? What are the pro's and con's of the two
configuration?

For this project I am using SS rectifiers. Were I using a tube rectifier
I would go with the center tap, of course.

- Paul
And here is the example everyone is eager to see. FWCT is awful at SUF of 0.415. PUF is still same as FWB (0.586) with cap input to filter since all the primary is in use. In a common amp or receiver PUF turns out better due to the loading of the heater windings which theoretically are 1.000. In reality less due the winding resistance.

But all can be justified since the power involved is small & the cct is simple & easy to build. But that adds a bit of expense & some weight.

A FWCT with choke input is somewhat better.

Cheers, John
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Charles[_7_] Charles[_7_] is offline
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Default Bridge or Center Tap?



"Paul D. Spiegel" wrote in message ...

For my next project I have acquired a transformer with two identical 450v
secondary windings. I could put the windings in parallel and use a bridge
rectifier. Or, I could put the windings in series and ground the coupling
for a 450-0-450 configuration to use with a pair of diodes.


If you choose parallel connected secondary windings, a power meter test is
one way to be sure. Fire up the transformer and measure the input power
(primary) with the secondary windings not connected. Repeat the test with
the secondary windings connected in parallel. If the windings are
identical, the primary power will not change.

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Phil Allison[_3_] Phil Allison[_3_] is offline
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Default Bridge or Center Tap?


"Charles"
"Paul D. Spiegel"
For my next project I have acquired a transformer with two identical 450v
secondary windings. I could put the windings in parallel and use a bridge
rectifier. Or, I could put the windings in series and ground the coupling
for a 450-0-450 configuration to use with a pair of diodes.


If you choose parallel connected secondary windings, a power meter test is
one way to be sure. Fire up the transformer and measure the input power
(primary) with the secondary windings not connected. Repeat the test with
the secondary windings connected in parallel. If the windings are
identical, the primary power will not change.



** Be far easier to do the test I suggested - OR, with your test, use a
simple current meter in the primary - OR just wait and see if the tranny
warms any more than usual.



.... Phil




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[email protected] paul.spiegel@att.net is offline
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Default Bridge or Center Tap?


Hey Paul, I think I may have corresponded with you a few years ago with
regard to my take on Crowhurst's Twin Coupled Amp. Was that you?


Anyway, here is my take on the FWB as opposed to the FWCT systems. An
important consideration for PS designers is something called 'Utility
Factor' of the various windings on the PT. Others have already noted the
FWB to be better if that connexion is possible. I've attched a numerical
example here for the secondary winding UF for the FWB with cap input
filter. Since there are no other windings the primary & secondary UF's
are equal.

Other examples will follow but in following posts since file size is
limited here in AudioBanter. But in summary the best UF for single phase
work is the FWB with choke input to filter. The lost power during the
conversion from AC to DC is in the form of the even order harmonics
(2nd, 4th, 6th...Etc) generated by the rectifying process.

You could check for the possiblity of circulating currents in the
parallel connexion of your PT secondaries as follows. Connect one end of
the secondaries in series opposition. Then with an AC VM check for any
voltage differance.


My guess is the voltages are near equal but with somewhat different
resistance, all OK to parallel permanently. Sounds like you have a PT
built from the core up to be series or paralleled, commonly available.
For example, Hammond lists many such devices.

Cheers to all, John

+-------------------------------------------------------------------+

|Filename: 100v Bridge BW.jpg |

|Download: http://www.audiobanter.com/attachment.php?attachmentid=300|

+-------------------------------------------------------------------+

--

John L Stewart


Hi, John. Yes, that was me who contacted you about the Twin Coupled amp. That project remains the best sounding stereo amp I've built yet. Thanks for your help.

I love choke input filters and use them as much as possible both for the greater current capability as well as the better voltage stability.

The pentode PP parallel amp I am currently building has two high voltage power supplies, one of each type: One FWB feeds a cap input for about ~600v on the EL34 output plates. A second FWB feeds a choke input for ~400v on the EL34 screens plus the input, gain, splitter, and driver stages.

The transformer is from Antek. This is the first project I have tried with one of their products.

Thanks to all of the RAT responses that convinced me to go with the parallel secondaries and FWB rectifiers.

- Paul
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Roger Jones Roger Jones is offline
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Default Bridge or Center Tap?

On Wednesday, 26 September 2012 22:34:04 UTC-4, Phil Allison wrote:
"Charles"

"Paul D. Spiegel"


For my next project I have acquired a transformer with two identical 450v


secondary windings.


(snip)

** Be far easier to do the test I suggested - OR, with your test, use a

simple current meter in the primary - OR just wait and see if the tranny

warms any more than usual.

... Phil


Do it the way Phil says... voltage or current measurement, voltage is a bit easier. The warming-up test is less precise, hard to remember how warm was warm!
Cheers,
Roger

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Phil Allison[_3_] Phil Allison[_3_] is offline
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Default Bridge or Center Tap?


"Roger Jones"
Phil Allison wrote:
"Charles"
"Paul D. Spiegel"

For my next project I have acquired a transformer with two identical
450v


secondary windings.


(snip)

** Be far easier to do the test I suggested - OR, with your test, use a

simple current meter in the primary - OR just wait and see if the
tranny

warms any more than usual.


Do it the way Phil says... voltage or current measurement, voltage is a
bit
easier.
The warming-up test is less precise, hard to remember how warm was warm!



** All you need to do is measure the resistance of the secondary winding
when at room temp and then when it has warmed.

The higher the resistance, the warmer the windings are getting.


..... Phil



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