| trustalbini |
Hey Everyone!
Just have a quick question:
How many watts should I assume I'm getting when I buy a transformer described as "300-0-300"? 300 or 600?
Also,
Does anyone have an idea as to how much voltage swing I should account for when designing the input section of a tube phono preamp? The cartridge is a MM type, something like a Goldenring Elan...
Thanks!
Dan |
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| ShiFtY |
I think 300-0-300 is the VOLTAGE rating, it means the secondary is 600V with a centre tap. With a normal full-wave tube rectifier and a C-L-C filter, you will get a maximum of 1.2 x 300V = 360V DC. You can tweak this a little by altering the value of the first cap.
With a bridge rectifier and CLC filter, (leaving the centre tap unused), you will have about 600 x 1.414 or so, so about 840VDC. (More or less!)
The key thing to look for in a tranny is the current, for example 300-0-300 100mA. This means you can draw 100mA from that winding indefinitely without failure.
If you multiply the voltage by the current, you get a rating in VA (volt-amps; not watts because no power is transferred in some cases)
A great tool to design power supplies is the Power Supply Designer II at www.duncanamps.com
While you are there download their tube database, its incredibly useful as well. |
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| jackinnj |
I posted the approximation of VA capacity vs core size. I will readily admit to being too lazy to find out where I put it -- must'a been two months ago.
jack |
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| gammelmalle |
I agree with ShiFtY that its the voltage, so you really need more info on the tranny. VA or Amp of secondary OR weight. Knowing the weight you can estimate the VA (It's actually the same as measuring the center core)
Cheers,
I'm actually sitting here with a beer and celebrating my birthday!
björn |
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| fdegrove |
Hi,
| quote: | | Does anyone have an idea as to how much voltage swing I should account for when designing the input section of a tube phono preamp? The cartridge is a MM type, something like a Goldenring Elan... |
A decent phonostage will usually "swing" about 10 to 30 volts peak depending how it's designed.
Don't know why you ask though...seems to me the obvious question to put is: what's the amplification factor I need to design for?
| quote: | | How many watts should I assume I'm getting when I buy a transformer described as "300-0-300"? 300 or 600? |
That would depend on the ampere rating, for instance;
Take a 0-300VAC xformer at 1A rating, that would be a 300VA xformer capable of delivering 300W max.
A 0-300VAC 2A would be 600W, and so on.
Simple as that.
Cheers,;) |
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| TNT |
A decent phonostage will usually "swing" about 10 to 30 volts peak
What ? Are You kidding ? |
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| fdegrove |
Hi,
| quote: | | What ? Are You kidding ? |
No I'm not.
I even have a preamp capable of swinging 120V P-P without batting an eyelid.
Powersupply design is everything when it comes to dynamic range...
I do get the feeling you guys are misunderstanding the issue though...:confused:
Cheers,;) |
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| trustalbini |
Hi Guys,
Yeah, I did mean Volts NOT Watts. Sorry. Thanks for the help.
Dan |
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