Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on January 18, 2011, 11:32:37 am
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Which are the differences about a B+ obtained via a standard bridge with condenser
and B+ obtained via doubler - triplers .................
naturally the consumption seen from the transformer is duplicate, tripled and so on
but which other differences ? different ripple ............. different frequency of ripple ?
and also
with SS bridge and condenser the assumption is to multiply for 1.4 so AC100v * 1.4 = DC140v
but what happen if is used a doubler, a tripler, a quadrupler ?
AC100v * 2 = DC200v
AC100v * 3 = DC300v
or instead it is
AC100v * 2 = DC240v
AC100v * 3 = DC340v
Very confused about the math is back to this way of rectify :rolleyes:
Kagliostro
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http://www.play-hookey.com/ac_theory/ps_v_multipliers.html
A doubler for all intents and purposes: Vout = 2Vpeak-(voltage drop of the diodes) Of course you may need to factor in some loading drop too. Have you played with Duncan's PSU Designer 2? It has a doubler circuit but no tripler. Doublers are cool but get wonky fast under higher current conditions. For example if you ave a 25V 20mA transformer, you should be able to get 49VDC at 10mA using a doubler constructed from 1N4007's but if you're really demanding 10mA, you're gonna have additional sag. Yeah we like sag in guitar amps up to a point. It's probably safe to assume that doublers double the sag too. IMO, triplers and beyond should be avoided 99 times out of 100. Suppose you needed 300V @ 100mA. Your PT would be 100V @ 300mA. It's like trying to seesaw with a fat man.
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http://www.play-hookey.com/ac_theory/ps_v_multipliers.html
A doubler for all intents and purposes: Vout = 2Vpeak-(voltage drop of the diodes) Of course you may need to factor in some loading drop too. Have you played with Duncan's PSU Designer 2? It has a doubler circuit but no tripler. Doublers are cool but get wonky fast under higher current conditions. For example if you ave a 25V 20mA transformer, you should be able to get 49VDC at 10mA using a doubler constructed from 1N4007's but if you're really demanding 10mA, you're gonna have additional sag. Yeah we like sag in guitar amps up to a point. It's probably safe to assume that doublers double the sag too. IMO, triplers and beyond should be avoided 99 times out of 100. Suppose you needed 300V @ 100mA. Your PT would be 100V @ 300mA. It's like trying to seesaw with a fat man.
The doubler is a combination of doubling / smoothing and full wave bridge. Therefore it is double the voltage x 1.4 and then add sag.
I've quite a bit of experience with quadruplers. From experience, a measured 68volts through a quadrupler should be 381ish. In reality it is closer to 360 volts. When run near the edge there is significant sag which approaches the sag you would get from a valve rectifier.
At the same time, the current is divided by the level of doubling and divided by 1.4. So if you needed 100ma through a quadrupler then you would need 560ma to begin with.
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I have used voltage multipliers in many amplifier builds without problems, most recently in a set of four amplifiers I called the "holiday family". Details of the first in the series are here: http://www.guitargear.net.au/discussion/index.php?topic=26388.0
The power supply used in these amplifiers was a voltage quadrupler:
(http://i497.photobucket.com/albums/rr333/valvetone/tio%2018/Tio18PSU.gif)
The following calculations will be rounded to sensible levels of accuracy, and will ignore effects such as diode voltage drops and transformer regulation.
The power transformer is 56VAC @ 2.4A.
So in a quadrupler, the output voltage is 56 * 1.4 * 4 = 314 volts DC.
The available output current is 2.4 / 1.4 = 1.7 Then 1.7 / 4 = 0.425 or about 420mA.
Actual B+ voltages measured in the amplifier mentioned above were:
1. At turn-on with cold valves: 334
2. Quiescent - valves warm: 319
3. At maximum sine-wave output: 315
4. At max clipping - i.e. square wave: 311
So the theoretical figure matched the observed results fairly well.
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MANY THANKS Butterylicious - Moody - Darryl
about math and real world test I think I've understand
but what about noise & Co. ?
In my mind a simply SS rectify gives ripple at the same frequency of the AC Line - 50Hz here in Italy
but which is the ripple frequency using a doubler or quadrupler ?
the 50Hz will rise to 100Hz and 200Hz ?
this higher frequency ripple isn't more difficult to be eliminated than a lower frequency ripple ?
Are these only my conjectures ? :rolleyes:
Thanks
Kagliostro
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I have used voltage multipliers in many amplifier builds without problems, most recently in a set of four amplifiers I called the "holiday family". Details of the first in the series are here: http://www.guitargear.net.au/discussion/index.php?topic=26388.0
The power supply used in these amplifiers was a voltage quadrupler:
(http://i497.photobucket.com/albums/rr333/valvetone/tio%2018/Tio18PSU.gif)
The following calculations will be rounded to sensible levels of accuracy, and will ignore effects such as diode voltage drops and transformer regulation.
The power transformer is 56VAC @ 2.4A.
So in a quadrupler, the output voltage is 56 * 1.4 * 4 = 314 volts DC.
The available output current is 2.4 / 1.4 = 1.7 Then 1.7 / 4 = 0.425 or about 420mA.
Actual B+ voltages measured in the amplifier mentioned above were:
1. At turn-on with cold valves: 334
2. Quiescent - valves warm: 319
3. At maximum sine-wave output: 315
4. At max clipping - i.e. square wave: 311
So the theoretical figure matched the observed results fairly well.
Darryl, may I ask what the measured voltage of the 56 volt transformer is when actually plugged in? I have noticed that many of the 30v transformers for example are in real life 34 or 35 volt even when wall voltage is very close to 240 volt exactly?
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but which is the ripple frequency using a doubler or quadrupler ?
There are different kinds of voltage multiplier.
Some are half-wave, so the ripple will be 50Hz.
Some are full-wave, so the ripple will be 100Hz.
However, there are some multiplier circuits that are combinations of full-wave and half-wave, so you can get asymmetrical ripple which is both 50Hz and 100Hz!
I devoted a chapter to voltage multipliers in my book.
http://www.freewebs.com/valvewizard2/book2.html
{EDIT -- untangled "/quote" -- PRR}
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MANY THANKS Merlin
There are different kinds of voltage multiplier.
Some are half-wave, so the ripple will be 50Hz.
Some are full-wave, so the ripple will be 100Hz.
However, there are some multiplier circuits that are combinations of full-wave and half-wave, so you can get asymmetrical ripple which is both 50Hz and 100Hz!
That is OK
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I devoted a chapter to voltage multipliers in my book.
That of my order for your second book was becoming a "Never End Story"
I ordered it to my supplier the 18/12/2010
here:
http://www.libreriauniversitaria.it/c_power_search.php?shelf=BEN&q=merlin+Blencowe&submit=
the 14/01/2011 they sent me a message : "the book at the moment is not momentarily available from our suppliers"
the 14/01/2011 I reordered the book, hoping it will be soon available
the 17/01/2011 I received another message: "the book you previously ordered is now available"
today (20/01/2011) if I look to my order I read: Open, but not delivered :sad:
Really I'm waiting to read that book, but it seems I must wait some other time ..............
Kagliostro
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Today I got the new Merlin's PS Book :grin: :grin: :grin:
I think I've something to read for the next days
Kagliostro
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kagliostro,
Hey, you got it. :grin: One of these days I've got to get around to ordering that book too.
Brad