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The All-New WA1GFZ MOSFET Audio Driver - Pics and Working!




 
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Author Topic: The All-New WA1GFZ MOSFET Audio Driver - Pics and Working!  (Read 20361 times)
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steve_qix
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« Reply #25 on: January 05, 2011, 11:24:32 AM »

As I'm sure most folks here know, I have layed out a LOT of boards - the whole class E board set (4 revs), the class H modulators (3 of them, with multiple revs).  These things take a lot of time to lay out and proof, then you have to have protos made to ensure there are no errors, etc. etc.

I just designed and built a direct coupled audio driver for class B grids (a completely different design, but still, similar in complexity) - it's not bad at all to point-to-point wire - no more complex than any tube audio driver project or a tube RF driver, etc.  The heat and high voltage are not board-friendly.  Anyone who has built tube equipment will have not trouble whatsoever with this project.  It's the same, without the heated cathodes!
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W2XR
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« Reply #26 on: January 05, 2011, 11:39:30 AM »

Good show, Frank.

The GFZ MOSFET audio driver will make a BIG difference and BIG bang for the buck in any BIG plate modulated AM transmitter. That's BIG news! Get rid of the tube drivers, backwards audio transformers, interstage transformers, etc.   Not only is it very heat-efficient and has little phase shift, but is small with just one supply required. Excellent performance with negative feedback built in - and easy to build, esp with a PC board.

Considering how much time and effort is needed to put a big plate modulated rig on the air, $100 for a custom board like this is a bargain in comparison.  No way to duplicate it for less once time and actual cash outlay is figured in for a small run of boards.

One volt of audio in = audio drive and fixed bias to the modulator grids, with a negative feedback loop back to the input..

If this board gets put to widespread use, it could revolutionize audio driver technology in the AM community. We might even be able to take over the whirl!... Grin

Disclaimer: Mr Vu has no financial involvement in Mr Carcia's proposed PC board project - your mileage may vary - the individuals portrayed here are actors - offer expires Dec 31, 2011

T

Well put, Thomas!

I have given my committment to Frank to purchase two of these FET audio driver boards.

$100.00 each is a very reasonable price to pay for an item such as this, when you consider all of the non-recurring engineering Frank has to go through to bring this board to market, such as the board layout, creation of the artwork so the board can be professionally fabricated, schematic capture, etc., and Frank is completely entitled to recover these costs in their entirety.  And because the quantity of the build is limited, the recurring cost is naturally significant. I know this from having sheetmetal parts fabricated for my various radio creations and restorations, as well as from my professional experience.

Come on guys, step up to the plate and give a committment to Frank today for your driver board. Be the first one on your block to take advantage of the technical benefits this circuit will provide in virtually any high-power plate modulated transmitter!

Don't delay, as quantities are limited. And if you place your order within the next ten minutes, we'll also include free with your order........

This offer is void where prohibited.

And I too have no business affiliation with Frank in this endeavor. I am only providing my encouragement to him.

73,

Bruce
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W7SOE
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« Reply #27 on: January 05, 2011, 12:19:25 PM »

Sorry guys, I have missed this thread.....

The board has been done for some time.  I just needed to increase the clearance between the traces.  If there is enough interest I will order a set of boards....

If someone else wants to do it that is fine too.


Rich


* audio_driver.gif (34.57 KB, 485x822 - viewed 524 times.)
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W7SOE
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« Reply #28 on: January 05, 2011, 12:38:22 PM »

I requested a quote from a PCB board house.  If I can get ten people to buy in, I can sell them for $35.


Rich


Tom,
   Since it will be several months before my 813 rig sees electrons I cannot test the board until then.  I have mine all built up including external caps, pots, and quick connects.  Would you be game for testing it in your rig?   Undecided

I will pay shipping both ways...


Rich
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K1JJ
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« Reply #29 on: January 05, 2011, 02:22:46 PM »

Rich,

I hesitate to test new prototypes on the 4X1 AM rig simply because the 4-1000A modulators are configured in tetrode operation (screen voltage, high gain) and very sensitive to mistakes.  Audio parasitics, improper negative feedback, etc = ruined mod iron or worse if not perfect.

You might check with Bruce/XR who uses low gain 833A triodes and is probably motivated to take the risk since he is looking to acquire this driver board.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed. 

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W7SOE
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« Reply #30 on: January 05, 2011, 02:29:23 PM »


You might check with Bruce/XR who uses low gain 833A triodes and is probably motivated to take the risk since he is looking to acquire this driver board.


How about it Bruce?

;-)

Rich
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DMOD
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« Reply #31 on: January 05, 2011, 08:52:17 PM »

I am in for at least one; I plan on driving a pair of 807's I recently acquired.

Let me know where to send the stash, eh cash!  Grin

Phil - AC0OB
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Patrick J. / KD5OEI
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« Reply #32 on: January 07, 2011, 08:06:41 PM »

In the original post, it was said it was for driving a pair of 4-1000's. It looks like it would also be able to drive a pair of 3-500Z's as a modulator or a pair of tetrodes (807's and 813's were mentioned) in the "special class B circuit" (grid 1 and 2 tied together as one grid). So long as no more than about +300V is needed peak per grid. Is this right?
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« Reply #33 on: January 07, 2011, 09:06:09 PM »

Not quite 300 volts peak due to circuit losses minus gate threshold voltage of about 4 volts. It should handle an 833.
Each output will swing close to 300 volts peak to peak. so in the case of the 833 with about -90 volts of bias it will swing close to 200 volts positive per tube.
Operating above +/- 300 volts would be pushing the 11N90 FETs a bit and I would be concerned with the 630V coupling caps. Above that voltage rating the price jumps up a lot.
I bet the circuit could be configured with high voltage IGBTs if one needs even more voltage swing. A bunch of resistor values would need changing.
The 11N90 will do 11 amps so as long as good heat sinking is part of the construction there will be no problem driving any tube. It is running class A.
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