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Old 28th December 2008, 05:01 PM   #1
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Default This power supply ok?

Anyone see any problems with the following supply? Iím trying to use a power transformer that has no secondary center tap. V1 and V2 will be TV dampers of the same type and are present to provide a B+ delay while the filaments warm up.

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Old 28th December 2008, 05:39 PM   #2
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D3 is in parallel with D5, D6 in parallel with D1. The full secondary voltage is presented to B+1 and ground through the bridge. Your B- will be at best, 0V.

Sorry, this won't work.
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Old 28th December 2008, 06:42 PM   #3
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Thanks, Iain. I might be overthinking this. Is the following any better?

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Old 28th December 2008, 07:41 PM   #4
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no....won't work...sorry, you B- will still be 0....
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Old 28th December 2008, 07:46 PM   #5
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Yes, that performs equally well for less cost

Your only options are:
A: to split the bridge output using resistors (as you are doing for B+1 and B+2) Then the bridge output provides B+1 and B-, you use resistors to create 0V and B+2. This is messy, wastes power and creates soggy(high impedance) rails.

B: use some kind of switched mode PSU to create the -ve additional rail from the B+1 rail. If B+1 is high voltage then this is ugly.

C: get a proper transformer.

Sorry, but a single winding really only produces a single rail. There's no free lunch even when you DIY
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Old 28th December 2008, 11:56 PM   #6
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Will a second HV winding help? How's the following?

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Old 29th December 2008, 12:05 AM   #7
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http://www.aikenamps.com/BackBiasing.html
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Old 29th December 2008, 12:28 AM   #8
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Quote:
Originally posted by astouffer
http://www.aikenamps.com/BackBiasing.html

I was just going to suggest that little trick.
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Old 29th December 2008, 01:22 AM   #9
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How much B- current do you need? You may be able to use a half-wave rectifier capacitor coupled to one end of the winding.
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Old 29th December 2008, 02:26 AM   #10
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Interesting article on back-biasing, but I unless I'm missing something this won't work in this case since my secondary winding has no center tap.

Tom, current will not exceed 10 ma. Is that within reason for what you're suggesting?
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