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Old 2nd May 2006, 10:31 AM   #1
kskr is offline kskr  Hong Kong
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Join Date: Jun 2005
Location: HK
Default Calculations for new Power transformer

Hello everyone,
It's been more than a week I can't see colors.(since my amp
is out of service )


Sad to say that my power transformer(250-0-250) is dead.
It was on a two-channel, 1 x 12at7 + 2 x 6v6 poweramp(diode Rectified, Pi CLC filter)

I think it consumes ~110ma for H.V. section.
And It's voltage after the 1st Cap. was ~300

I now got a new Power Transformer(330-0-330 300ma, 5V 4A),
and bought a 5u4GB. So I think it'll be ~400V regulated?

My question is:

1) what's the voltage rating for filter cap I've to use?
>450V?

2) what's the estimated value(ohms & watts?) of the dropping
resister after the first filter cap?


3) I heard people said, if you got a higher rating's trans.,
use smaller value(uf) cap. for filtering, is it right?
(I think I'll purchase a 7-10H choke)

4) For the 5u4GB, is it alright use either pin(2/4) for H.V. out?

any help is great!!
Many thanks!!

Kenny
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Old 2nd May 2006, 10:49 AM   #2
diyAudio Member
 
Join Date: Feb 2005
Location: leeuwarden, netherlands
Hi,

1) what's the voltage rating for filter cap I've to use?
preferrably larger....630V....better safe than sorry...

2) what's the estimated value(ohms & watts?) of the dropping
resister after the first filter cap?

depends on how much you wanna lose, would be nice to see a schematic...burning voltage away after the first rect. cap will produce lots of heat....

Download: Duncans power supply designer!, you can even put YOUR new transformer into the program...
you can also see what the sec. resistance does with peaks

>>(I think I'll purchase a 7-10H choke)
better than a resistor...

you mean pin 4&8...... i don't think that to be a problem, maybe someone knows a better answer for that one....

greets!!
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Old 3rd May 2006, 12:15 AM   #3
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Alain Dupont's Avatar
 
Join Date: Sep 2003
Location: Paris - France
kskr,

Take a look at:
http://www.angela.com/catalog/how-to/Single.6V6.html
http://www.audiotropic.net/WillsAmp/
http://audiotropic.netfirms.com/audio.html

Ithink you'll have matter to define a new transfo.

Regards.

Alain.
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Old 3rd May 2006, 09:29 AM   #4
kskr is offline kskr  Hong Kong
diyAudio Member
 
Join Date: Jun 2005
Location: HK
Wow, thanks for quick replies!
Also, info is great!

Frankly speaking, I've always tried searching schematics,
for 6v6s, but just couldn't find one that has
the transformer that has such a high voltage,
I know it'll fit on 300B circults perfectly but I just
couldn't afford it.


Last night I tried to estimate my dropping resistor value.
With my limited maths calculation(V=IR thing),
If I got it right, according to my amp's power

rating(~110ma & ~33W), I need a resistor
consuming 110ma and drop the unwanted part of voltage,
say..100V. So it'd be ~900ohms & 11W(15W/20W for safety?)

Any help appreciated!

Many thanks,
Kenny
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