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Old 18th December 2012, 10:52 AM   #1
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Default Power supply, heater questions...

Hi,

I think, a lot of you own "Morgan Jones", Valve Amplifiers.

I read some stuff, and now I have some (stupid) questions:

1. Choke HT supplies: page 318, fig. 5.18b: How do I determine the 265 ohm and the 220 nf as "perfect" values??? Howto measure / simulate best? (R=265 ohm is the result to optimize Q, see page 322, but how to determine C to 220nf?)

2. HT supply, a lot of general questions:
- I refer to page 374, fig 548
- Which diodes to use? I can find many 1000V types... How do I determine the ideal capacity across a diode to improve spiking? Recommended diodes, formula to calculate cap in accordance to required current...
- There is a box around choke and resistor. this is optimizez according to page 322. The additional resistor adjusts the voltage??? And how do I determine optimized for the caps to ground before and after this arrangement? The first cap does also rise the voltage? Do we need symmetry at all (220nf before, 220nf after???)
- Next question to the LT supply (fig 5.48) The small filter choke. Must the pinss be used so that the constant current cancels???

Sooo many questions...

Dirk
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Old 19th December 2012, 03:09 PM   #2
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Quote:
Originally Posted by HVfanatic View Post
Hi,

I think, a lot of you own "Morgan Jones", Valve Amplifiers.

I read some stuff, and now I have some (stupid) questions:

1. Choke HT supplies: page 318, fig. 5.18b: How do I determine the 265 ohm and the 220 nf as "perfect" values??? Howto measure / simulate best? (R=265 ohm is the result to optimize Q, see page 322, but how to determine C to 220nf?)
265 ohms is a typical DC resistance of a choke as explained in other text. The 220nF is found empirically to provide sufficient snubbing in most cases.

Quote:
2. HT supply, a lot of general questions:
- I refer to page 374, fig 548
- Which diodes to use? I can find many 1000V types... How do I determine the ideal capacity across a diode to improve spiking? Recommended diodes, formula to calculate cap in accordance to required current...
1N4007 will be all you need for most HT supplies but you can use the fast recovery versions if you wish.

I think this power supply is over designed given the application. There is no need to start with 675V secondary transformer.

Quote:
- There is a box around choke and resistor. this is optimizez according to page 322. The additional resistor adjusts the voltage???
It adjusts the Q as described in the text.

Quote:
And how do I determine optimized for the caps to ground before and after this arrangement? The first cap does also rise the voltage? Do we need symmetry at all (220nf before, 220nf after???)
As noted above, 220nF is found empirically to give good snubbing.
Quote:
- Next question to the LT supply (fig 5.48) The small filter choke. Must the pinss be used so that the constant current cancels???
So common mode interference cancels.

Cheers

Ian
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Old 19th December 2012, 10:05 PM   #3
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Hi Ian, thanks for clarification.

one question: I always thought, that chokes store energie due to magnet field. I thought, that positive and negative windings remove magnetisms, therefore remove inductivity. So common mode choke has no inductivity, just cancels common mode disturbance?

Regs, Dirk
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Old 19th December 2012, 10:11 PM   #4
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Another point: Morgan Jones uses diodes across the rectifier diodes. Which value is required for LT, which for HT. How is this value related to the current drawn?

Dirk
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Old 19th December 2012, 10:31 PM   #5
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Quote:
Originally Posted by HVfanatic View Post
Hi Ian, thanks for clarification.

one question: I always thought, that chokes store energie due to magnet field. I thought, that positive and negative windings remove magnetisms, therefore remove inductivity. So common mode choke has no inductivity, just cancels common mode disturbance?

Regs, Dirk
Don't forget the current flows in opposite directions in each winding so it does have inductance.

Cheers

Ian
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Old 19th December 2012, 10:32 PM   #6
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Quote:
Originally Posted by HVfanatic View Post
Another point: Morgan Jones uses diodes across the rectifier diodes. Which value is required for LT, which for HT. How is this value related to the current drawn?

Dirk
Do you mean capacitors across diodes?

Cheers

Ian
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Old 20th December 2012, 12:28 PM   #7
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Ok, so top 5 I was right.

Yes, I mean caps across diodes... What rules obey here?

Regs, Dirk
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Old 20th December 2012, 08:34 PM   #8
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Quote:
Originally Posted by HVfanatic View Post
Ok, so top 5 I was right.

Yes, I mean caps across diodes... What rules obey here?

Regs, Dirk
I don't know for the set of series diodes but I would expect 100nF would be sufficient. The diodes will turn of a slightly different times which means one capacitor might be required to sustain the whole peak secondary voltage. Rate them accordingly.

Cheers

Ian
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Old 21st December 2012, 09:59 PM   #9
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Hi Ian, my wording was misunderstanding (sorry), I talked about caps across single diodes to reduce switching effects. How do I size them, of course approbriate voltage, but what capacity???

Dirk
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Old 22nd December 2012, 10:30 PM   #10
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Quote:
Originally Posted by HVfanatic View Post
Hi Ian, my wording was misunderstanding (sorry), I talked about caps across single diodes to reduce switching effects. How do I size them, of course approbriate voltage, but what capacity???

Dirk
Generally 100nF is used although I have seen some designs use 10nF.

Cheers

Ian
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