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Old 18th June 2007, 10:34 PM   #1
jarthel is offline jarthel  Australia
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Default reversing polarity in regulated B+ and other question

here's the original schematic: http://img227.imageshack.us/my.php?i...00bbpsudn3.gif

Here's the new schematic: http://img514.imageshack.us/my.php?i...0bbpsu1iw3.gif

The original schematic has the 420V at the top and 0V at the bottom. I would of course get a positive voltage.

Is it safe/okay to reverse the connection (as shown in the new schematic above) so that I get a negative supply?

If yes to the question above, is it safe/okay to connect the 0V point of the negative supply above to the 0V point of a +1000V supply? (i.e. connecting the 2 ground points together)

Thank you for help
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Old 18th June 2007, 10:39 PM   #2
billr is offline billr  New Zealand
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Hello

what you have there is a floating power supply, so as you rightly surmise, you can label the outputs as you please.

If you want to reference this power supply to some other, then you can just connect the top wire to the 0v line of the other power supply, and what is originally shown as the 0v line on the floating supply, now becomes the -420V line.

hope that this helps.

Kind regards

bill
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Old 19th June 2007, 12:43 AM   #3
kevinkr is offline kevinkr  United States
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I've used series pass tube regulators as negative supplies, note this requires a dedicated secondary as the winding floats..

I used a 6U8A based design as a -200V bias supply in my 300B PP project about 8yrs ago, this might provide some inspiration for a design of your own. Note that this circuit can provide up to 20mA of output current, but not much more, other pentode/triode combos can provide more current if required, if you go this route just be sure to choose one with a moderate to high mu triode as that's used as the error amplifier in my design. (The higher the better.) Watch Vhk ratings as well.

The schematics are on my site under the VTV 300B PP amplifier article.

http://www.kta-hifi.net/projects/amp...mp/300bpp.html

The link to the article and schematics is at the bottom of the page.
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Old 19th June 2007, 02:48 AM   #4
jarthel is offline jarthel  Australia
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Quote:
Originally posted by kevinkr
I've used series pass tube regulators as negative supplies, note this requires a dedicated secondary as the winding floats..

I used a 6U8A based design as a -200V bias supply in my 300B PP project about 8yrs ago, this might provide some inspiration for a design of your own. Note that this circuit can provide up to 20mA of output current, but not much more, other pentode/triode combos can provide more current if required, if you go this route just be sure to choose one with a moderate to high mu triode as that's used as the error amplifier in my design. (The higher the better.) Watch Vhk ratings as well.

The schematics are on my site under the VTV 300B PP amplifier article.

http://www.kta-hifi.net/projects/amp...mp/300bpp.html

The link to the article and schematics is at the bottom of the page.
just a question Kevin.

Is the principle of inverting the connection the same to get the negative supply out of positive supply? Is this true for any regulated B+?

Thank you

ps. I would like to stick to 6as7/6080 as I have a stack of 6as7 at home already
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Old 19th June 2007, 04:03 PM   #5
kevinkr is offline kevinkr  United States
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Hi Jarthel,
Yes they are reversible, the key is that the entire supply should be designed to float, and then you just ground one or the other output depending on the output polarity you need.

The 6AS7 is a fine pass element particularly where relatively high currents are needed with relatively little overhead (drop out voltage) - make sure that you have at least 100V - 125V margin with the 6AS7/6080/6336 family of tubes for best performance. Should you need very low ripple use a high gain error amplifier like a cascode and/or use a CLC in front of the regulator. (I generally use both or a pentode connected pass element.)

Gas tube references like the 5651 and 85A2 are very temperature stable, and have pretty good voltage tolerances too, but exhibit much higher dynamic impedances than zeners and this may result in loss of gain from dc up to the point where the bypass cap starts to have an influence. (Note that too big bypass caps directly across the reference will turn gas tubes into neon relaxation oscillators. 0.047uF is the highest value I recommend.) For maximum ripple rejection I would probably use a zener when the reference is in the cathode circuit of the error amplifier.
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Old 20th June 2007, 12:05 AM   #6
jarthel is offline jarthel  Australia
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Quote:
Originally posted by kevinkr
Hi Jarthel,
Yes they are reversible, the key is that the entire supply should be designed to float, and then you just ground one or the other output depending on the output polarity you need.
Hi Kevin.

Could you explain what you meant by "float"?

I am thinking/imagining that the negative terminal of the negative supply IS NOT connected to the negative terminal of the B+ supply.

Is this correct?

Thanks again
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Old 20th June 2007, 01:19 AM   #7
billr is offline billr  New Zealand
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[QUOTE]Originally posted by jarthel
[B]

Hi Kevin.

Could you explain what you meant by "float"?

Floating means that the power supply is not grounded in any way. ie, the neither the negative nor the positive output are connected to a common earth point.

Which means that you can only measure the output of the power supply across it's output leads.

Hope this helps

bill
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