Large red help button.. or Just a bunch of questions

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Large red help button.. or Just a bunch of questions

Postby Sparky » Sat Nov 13, 2010 9:57 am

Well seems i joined some time ago, but what that signup was/is lost. So I'm not so new to this forum. But I have returned.

Lots of questions:

1. Using the 24 FET version, what power supply requirements are necessary to use it with the PWM rev D?
2. The latest version , 24 FET shows a current requirement of 25.6A, and is this correct because the power supply rev D shows an 8A transformer. A slight mismatch. Also I heard that the filter caps are on the small side uF-wise.
3. Can large mica caps be used for shunt caps like : Image or the 2 eared version: Image ?
4. Is the PWM rev D sufficient to modulate the 24 FET to 100%?
5. Full RF current passes through the efficiency board from the PWM? If so the traces look small for 26A.
6. A general clue as to what is grounded as common or what is not in assembly. For example driver to RF out I have down, i.e. seperate RG-175's to and fro. Anywhere else special grounding rules apply?
7. Does Kapton MT burn with an ordinary cigarette lighter? Frank? I'm also experimenting with your method as well.

As always, thanks. Tom KA1HNH
Last edited by Sparky on Mon Nov 29, 2010 9:17 am, edited 1 time in total.
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Re: Large red help button.. or Just a bunch of questions

Postby kf1z » Sat Nov 13, 2010 12:30 pm

1) 130 vdc, ( a 100-104vac, 1.5kva or larger xformer should do it)

2) The Rev D PWM transformer is based on a 8 or 10 FET RF deck.
20,000uF should be sufficient, but you CAN use more. The "feed-forward" on the PWM generator board
does a lovely job of cancelling any PS ripple.

3) Use the ATC100C series caps for shunt C. If you need some, I have them.

4) PWM Rev D, with all 5 IRFP260N and all 5 DSEI30-06 diodes will modulate a 24 fet rf deck to over 100% ( 150 + )

5) With a 24 fet deck, you bypass most of the current around the OL board.
Steve will clue you in on how he does that

6) Standard RF / audio grounding applies.. single point ground for the most part.

7) Kapton will char and melt (sort of) with a lighter..
I used the copper slab and Kapton for my 75 meter deck, works very well... but if it's a multi band rig, you need to ddesign that fixed
capacitor for the highest band, and you STILL need to switch in other caps for the lower bands...
I suggest using the ATC100C caps.... they are likely cheaper, and definately MUCH easier to use!


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Re: Large red help button.. or Just a bunch of questions

Postby Sparky » Wed Nov 17, 2010 10:00 pm

Wow, got busy there for awhile.... Thanks for the reply.
So a couple of more ???

Are the micas shown usable or not? Well aware of the ATC stuff, just trying to utilize a bunch of nos caps I have.

I've got 31,200 uF now.

Also bought some Kapton off Ebay and was trying to sample burn a piece to make sure it was the real stuff. Burns exactly as you said.

As far as bypassing current around the sensor, I'd like to know just how that's accomplished.

New question...Making up the outpoot transformer cores. I'd like to build them with copper tubes inside on a common 1/8" ss PCB. Is it a no-no to do so? How should the common foil be separated or not, or maybe just between the two phases? So, i.e. 4 cores per stack, 4 stacks of cores = 1 phase, the 4 more stacks of cores other phase, common foil to first 4 then common foil to second 4, where, if anywhere, to connect the top and bottom foils (assuming this is allowed with copper tubes)? Or will it self destruct of RF is applied?

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Re: Large red help button.. or Just a bunch of questions

Postby kf1z » Thu Nov 18, 2010 8:43 am

I don't know if those micas would work or not, to be honest.
I do know the ATC100C work VERY well. Doorknobs do not.


Transformer cores.
I do it that way, with brass tube for the primary, and PCB material.
However in your case, with higher power, I suggest connecting the tubes with copper or brass stip,
Instead of relying on the PCB copper.

Use the tubes as the primary for each individual transformer, use wire for the secondary.



Image
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Re: Large red help button.. or Just a bunch of questions

Postby Sparky » Thu Nov 18, 2010 1:26 pm

Her's what I have fabricated so far, 3/8"ID 1/2" OD copper. If you think I need it, although difficult, I guess I can add copper flashing to it:

Image

Also a crude non-artist's rendition of foil separation/core placement:

Image

Or:

Image

So is this correct? If so then I will cut the PCB to match.

The tool used to make these, with a 1/2 hour to get up to temp, I give you Big Daddy. Forget the Weller D550 It don't even make a dent:

Image

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Re: Large red help button.. or Just a bunch of questions

Postby kf1z » Thu Nov 18, 2010 5:42 pm

I would go with the second one , with the first one, the tubes would have to be the secondary..
Which would likely be ok, except for layout issues.
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Re: Large red help button.. or Just a bunch of questions

Postby steve_qix » Wed Nov 24, 2010 8:30 pm

Sparky wrote:Well seems i joined some time ago, but what that signup was/is lost. So I'm not so new to this forum. But I have returned.

Lots of questions:

1. Using the 24 FET version, what power supply requirements are necessary to use it with the PWM rev D?

You'll need (for 45V at carrier on the RF amplifier) a 10A transformer or thereabouts - a little over 1KVA minimum for 24 FETs at full power.
2. The latest version , 24 FET shows a current requirement of 25.6A, and is this correct because the power supply rev D shows an 8A transformer. A slight mismatch. Also I heard that the filter caps are on the small side uF-wise.

Oh, that power supply is specifically for a 450 watt transmitter. The REV D PWM output board, fully populated, will modulate a 24 MOSFET RF amp, no problem.

I use 64,000uF of filtering for 24 MOSFETs. The 25.6A is AFTER the PWM filter (use air core inductors). The actual power supply is required to furnish more like 8.5A at 135V for a 45V DC output @ 25.6A. Use a 10A / 1.3 KVA or larger transformer.
3. Can large mica caps be used for shunt caps like : http://www.surplustuff.com/images/cap004.gif or the 2 eared version: http://estoreoutwest.com/images/electronics/capacitors/4-52050JB.jpg?

They probably have too much internal resistance. Doorknobs are also not too good. Really, use the ATC Multilayer Ceramics.
4. Is the PWM rev D sufficient to modulate the 24 FET to 100%?

Yes, if fully populated.
5. Full RF current passes through the efficiency board from the PWM? If so the traces look small for 26A.

You need to use a shunt across the board. Ill furnish pictures.
6. A general clue as to what is grounded as common or what is not in assembly. For example driver to RF out I have down, i.e. seperate RG-175's to and fro. Anywhere else special grounding rules apply?


7. Does Kapton MT burn with an ordinary cigarette lighter? Frank? I'm also experimenting with your method as well.

Hmmmm. Don't know about that one!
As always, thanks. Tom KA1HNH
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