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Greg
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#46

Post by Greg »

Philip, I may be wrong but don't you have your battery +ive and -ive the wrong way round?
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pre65
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#47

Post by pre65 »

I hope not. :wink:

The idea is to make the grid negative compared to the cathode. The cathode is grounded (0v) so to get the 9v bias the grid has to be at -9v.

So that's why the neg terminal goes to grid, and positive to ground.
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Greg
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#48

Post by Greg »

OK, that's different to how I apply battery bias in my 300B PP and I thought Paul's original diagram suggested the reverse of how you've drawn it. You obviously know what you are doing :wink:
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Paul Barker
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#49

Post by Paul Barker »

Greg wrote:I thought Paul's original diagram suggested the reverse of how you've drawn it.:
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pre65
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#50

Post by pre65 »

I've built a PSU for the raw DC on my 26 filament supplies.

I ended up with a 50va 9v toroid and choke input using a Hammond 10mH @ 5A choke.

What confuses me is why putting a cap before the choke (tried 4uf to 20uf) seems to have no effect on the voltage. Is it because the choke size is so small ?

PSU designer seems to replicate my findings.
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Paul Barker
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#51

Post by Paul Barker »

9v/1,000 mA = 9 mH so your chokes cannot actually be 10 mH. The reality of the situation is you aren't achieving choke input so the choke simply cannot be 10mH so it isn't what it says on the tin.

I am not surprised.
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pre65
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#52

Post by pre65 »

Hammond call it a "reactor" but is than not a choke by another name ?

Fortunately, even without the extra cap the voltage I got is just about right.

If I need more I will go cap input.
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#53

Post by Paul Barker »

Yes "ReeeacTOOOORe must be Yankedandedoodle for choke. We might call it an inductor occasionally.
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#54

Post by Mike H »

Yes what you've got is just a RF filter, not an input choke.
 
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#55

Post by Mike H »

pre65 wrote:If I need more I will go cap input.
It is already cap input, you've just got 10mH between rectifier and the 1st cap.

That's why you can't get any change by putting an extra cap in front, it already is working as cap input.
 
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#56

Post by pre65 »

I read somewhere that if the windings of a centre tapped transformer are not of equal resistance it can cause problems.

1) Does that apply to primary and secondary windings ?

2) Does it still apply if the centre tap is only to join two windings in series ?

3) Is it a simple case of adding resistance to the lesser winding to "balance" things ?
The only thing necessary for the triumph of evil is for good men to do nothing.

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