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Old 26th May 2012, 05:07 PM   #1
srinath is offline srinath  United States
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Default 420vdc supply for a tube amp

I got a few cisco 6000 power supplies sitting round.
Now its a switching supply with a 1300w output and 42v, 12v 5v, 3.3 v etc.
However in it there is a 420vdc plug that supplies from 1 side to the other side - sorta an internal transfer point. I am looking for some way to power a tube amp with that - if possible.

Is there a tube circuit using 420vdc - Can I use it for my dynaco st70 which I have the circuit board only - no transformers at all and no chassis either.

Thanks.
Srinath.
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Old 26th May 2012, 05:26 PM   #2
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Not a good idea unless the output is totally isolated from the input. You'll see fireworks
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Old 26th May 2012, 06:17 PM   #3
12E1 is offline 12E1  United Kingdom
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I would go further - I suggest it could be a very dangerous idea (what astouffer meant, I think). Not only that, but how does that supply behave when the other rails are not loaded significantly? The 420V output is most likely not completely isolated (hence the danger), and could also be electrically quite noisy. Probably not the best choice for an audio application.
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Old 26th May 2012, 07:07 PM   #4
pergo is offline pergo  Italy
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easy to do with DC-DC step-up
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Old 26th May 2012, 10:16 PM   #5
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Just seen some 42V 100A computersupplies thrown out... I had some naughty plans for those too... but they had to be disposed off via official channels...

Sorry, back on topic
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Old 27th May 2012, 12:48 AM   #6
srinath is offline srinath  United States
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Default Hope so

Quote:
Originally Posted by pergo View Post
easy to do with DC-DC step-up
I thought, hope and wish so, its a clean 420vdc that whole thing is made for being super super steady and clean, after all it cost nearly 6 grand a few years ago.
So ... How do you do it, there is that circuit I got with the 420v shown ... can I just use this guy in that spot ?

Cool.
Srinath.
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Old 27th May 2012, 02:17 AM   #7
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To me,it sounds like the 420Vdc connector might be the rectified mains bus?
If so,it would be VERY dangerous to use that,as already mentioned,it's not isolated.
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Old 27th May 2012, 02:37 AM   #8
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Most large switching power supplies have active PFC. This is required in EU countries, and pretty common here. Large supplies have an active PFC stage which takes any supply voltage within its specified input range and steps it up to a constant regulated voltage that is higher than the highest specified input voltage. 300 volts is common for small power supplies found in home PC's. Larger supplies may use a higher voltage. This regulated high voltage then feeds the second stage which supplies the output voltages.

The active PFC stage in any power supply that I have been into operates DIRECTLY on the line (mains) input. Its output is NOT ISOLATED FROM THE LINE INPUT. It is usually a speciallized boost converter with its own PFC controller chip. I suspect that this may be the case with your power supply. You MUST verify no continuity between the 420 volt terminals and the line input before attempting any connection to them. Use of a non power supply can result in your entire audio system being energized with line voltage possibly causing a potentially lethal shock.
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Old 27th May 2012, 07:31 AM   #9
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This goes under the category of "solution in need of a problem".
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Old 27th May 2012, 08:50 AM   #10
pergo is offline pergo  Italy
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Quote:
Originally Posted by srinath View Post
I thought, hope and wish so, its a clean 420vdc that whole thing is made for being super super steady and clean, after all it cost nearly 6 grand a few years ago.
So ... How do you do it, there is that circuit I got with the 420v shown ... can I just use this guy in that spot ?

Cool.
Srinath.
in my hybrid amps i always use DC-DC step up, from +Vrail (usually 30 or 40V, for the BJT output stage).

If, after the DC-DC, you will add a capacitance multiplier (with low RC costant, so it will work also as soft-start), you will be absolutely quiet.
No hiss, no hum, etc...
I also use DC-DC for heaters

In my amps there are always 3 DC-DC converter (12-->+-40V, +40V --> 300V, +40V ---> 6.3V)

On Ebay you find the Nixie power supply, large as a dollar-coin, from 12V up to 450V@10mA or 225V@20mA.
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