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Old 22nd May 2006, 06:56 PM   #11
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the one important thing to realize when doing this is the power ouput is going to be limited by the maximum flux on the core.

Most toroids are designed to operate at a flux just under saturation so the most voltage you can put across the prmary is 230V@ the line frequency. Say you wanted a 5K ratio and sized the secondary to deliver 9V. This means you max voltage inot an 8 ohm load would be 9V or 10W at the line frequency. Cutting the frequency in half to get 25-30hz power you can only deliver 4.5V or 2.5W!

a good way to start this is to figure the power you need at 1/2 the line frequency and then work backwards to determine the load the transformer will provide and choose an appropriate tube.

Lets say you want 24w @ 30hz into 8 ohms (i'm in the us) This means you need 14V@ 30hz or 28V @ 60hz which translates to a 240:28 transformer or an 8.5:1 turns ratio. When you plug the 8 ohm load back inot this you get a primary impedance of 575 ohms which suggests the tube to use is a 6C33.

dave
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Old 4th June 2006, 09:39 AM   #12
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Default How to make a parafeed TX

If I wanted to ask to my manufacturer to make for me a parafeed transformer, what would be the specifications ?
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Old 4th June 2006, 12:01 PM   #13
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He may not have the expertise to do that for you.
You would need a really large core, with a high number of primary turns. If inter winding capacitance isn't going to be a significant issue, then he will need to interleave the primary and secondary windings. He may not be set up to do this as usually the primary winding is wound on the core before the secondary. This, I suppose, is why these transformers cost more !

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Old 4th June 2006, 12:31 PM   #14
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Elettronica Novarria is downtown Milano, so really near where I live.
My question was also about materials and so on.
If a parafeed transformer is conceptually the same as a PP transformer, primary-secondary interleaving should not be a problem
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Old 4th June 2006, 12:55 PM   #15
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Look like they could do it.

You need to decide what low and high level response is acceptable, what power you need at the average and lowest level. Then take that information to them and they should have computer models to do all the rest for you. If your going to get one custom wound don't waist your time reinventing the wheel.
Useful primary information can be got from the www.bottlehead.com

Good luck

Shoog
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Old 4th June 2006, 01:25 PM   #16
Giaime is offline Giaime  Italy
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Ciao Teodoro,

Novarria is a good transformer winder. His PP outputs are good for the price, maybe you can get away with one of those.
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Old 4th June 2006, 09:32 PM   #17
gemby is offline gemby  Croatia
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Guys, can you point me to some direction how to use mains toroid with SE amp, i am about to make SE amp with GU-50.
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Old 5th June 2006, 08:41 AM   #18
Gluca is offline Gluca  Italy
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Torroids are no good for SE amps! They are not gapped.

OH! Please note that if you are planning to build a parafeed amp using a torroid you should take care of the LC-OPT low freq resonance.

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Gianluca
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Old 5th June 2006, 09:29 AM   #19
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Default LC-OPT ...

... I'm lost !
What do you mean ?
Let me ask again the same (unanswered) question: if I ask for a (parafeed) transformer to my local manifacturer what are the characteristics I should ask ?
1. no gap
2. high primary inductance
3. low parasitic capacitances (i.e. pri-sec interleaving)
...
What else ?
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Old 5th June 2006, 10:58 AM   #20
Gluca is offline Gluca  Italy
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reflected load
max signal to handle
turns ratio
etc...

May I suggest to look at a known and working application? At the bottlehead.com or magnequest.com you can find ideas and support.

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Gianluca
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