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Old 30th January 2009, 06:58 AM   #1
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Default Choke load calculation...

Can anybody send me a link that explains how to calculate choke loads?

Thanks, Dirk
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Old 30th January 2009, 07:28 AM   #2
316a is online now 316a  England
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Go to vt52.com . Look at diycorner , tip and tricks , software tools and open platechoke.xls .

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Old 30th January 2009, 07:29 AM   #3
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This was written w/r/t/ attenuators, but the calculation is the same. From http://www.intactaudio.com/atten_FAQ.html

Quote:
The simplified approach is to determine the desired load taking into consideration the lowest frequency of interest and doing a few simple calculations. For example: If your source is a CD player with a 50 ohm Z-out and you want to adhere to the 1:10 ratio of source to load many suggest all you need ot do is pick a suitable low frequency (often 20hz) and plug the numbers into the Z=2piFL formula to get, 500=2*pi*20*L. Solving for L gives you a required 4hy inductance to provide a 500 ohm load to a 50 ohm source.
Substitute rp for the cd Z-out in the example.
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Old 30th January 2009, 08:16 AM   #4
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THANKS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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Old 30th January 2009, 09:51 AM   #5
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Hi,

I got so far:

Using a PL509 in Screen drive, I get Rp = 8000 Ohm.

I want the -3 db point at 50Hz, this means, I have to use a 25 Henry choke

Electrostatics need push-pull, so my choke must be wound with opposite coils, having a total of 50 Henry.

If I use 2500Volt as a power supply, I assume that I negnect the Ohmic resistance (Is this correct???). The tube can handle 40 Watt dissipation.

So 15mA of standing Current would be ok???

I haven't found any mu values for the tube in ETM? Somebody has values, comments to my thoughts???

Regs, Dirk
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Old 30th January 2009, 10:26 AM   #6
316a is online now 316a  England
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Quote:
Originally posted by HVfanatic
Hi,

I got so far:

Using a PL509 in Screen drive, I get Rp = 8000 Ohm.

I want the -3 db point at 50Hz, this means, I have to use a 25 Henry choke

Electrostatics need push-pull, so my choke must be wound with opposite coils, having a total of 50 Henry.

If I use 2500Volt as a power supply, I assume that I negnect the Ohmic resistance (Is this correct???). The tube can handle 40 Watt dissipation.

So 15mA of standing Current would be ok???

I haven't found any mu values for the tube in ETM? Somebody has values, comments to my thoughts???

Regs, Dirk
If you can find it , the Svetlana EL509 datasheet has screen curves . You should have no problems obtaining 50H with a centre-tapped choke . You may find a push pull output transformer will get your project up and running . I used a ultralinear transformer a while ago strapped as a stepup autoformer . The UL taps were connected to the anodes of the output valves and the output to the stators taken directly from the anode taps . It worked well with my DIY treble panels , I don't know how well this will work with a full range panel though

316A
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Old 30th January 2009, 12:43 PM   #7
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As I mentioned in your other thread, Jack at Electra-Print have made a PP-pair for me.

About current you must know the ESLs capacitance at 20kHz to calculate.

Also I doubt EL519 can take 2,5kV continous even at low currents.
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Old 30th January 2009, 01:00 PM   #8
SY is offline SY  United States
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I prototyped a PP choke-loaded amp for my ESLs a couple of years ago- if you have a step-up transformer (I used the LF one for the Acoustat MK121), just turn it around and use the secondary to load the tubes. The primary can be left open or be shunted with a damping network. Balanced, center-tapped, known-good at high voltage, known high enough inductance for the panels, what's not to like?
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Old 30th January 2009, 01:36 PM   #9
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Old 30th January 2009, 02:47 PM   #10
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@316a: I don't understand. I could understand if you used the EL519 as pentode. So I would take the signal from the anode leads...

But you connect the UL leads with the valve anode, and the esl with the Anode leads...

In case of a screen drive, I would only use the anode leads...

@revintage: Curcio uses pl509 as srpp with 4kv, other designs with more than 5kv... (SRPP)

I took the choice of 2,5kv and 15mA because of max. dissipation...

@sy: Isn't it a problem that the primaries increase maybe capacitive effects??? Why should I use damping elements?

@all: So all of you prefer choke loading to srpp??? Reasons???

Regs, Dirk
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